Mobile communication system, mobile terminal and base station

ABSTRACT

A mobile communication system capable of easily notifying the interference-related information and avoiding interference in a situation in which a macro cell and local nodes are deployed to coexist. In the system, a macro cell (eNB) notifies, via user equipments (UEs) present in a coverage, HeNBs present in the coverage of the interference-related information related to the interference to a physical resource to be used, for example, a high interference indication (HII) and an overload indicator (OI).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/039,793 filed Jul. 19, 2018, which is a continuation of U.S.application Ser. No. 15/133,684 filed Apr. 20, 2016 (now U.S. Pat. No.10,051,642 issued Aug. 14, 2018), which is a divisional of U.S.application Ser. No. 13/578,694 filed Aug. 13, 2012 (now U.S. Pat. No.9,350,496 issued May 24, 2016), which is a National Stage ofPCT/JP2011/052729 filed Feb. 9, 2011, and claims priority to JapanesePatent Application No. 2010-028637 filed Feb. 12, 2010. The entirecontents of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a mobile communication system in whicha base station performs radio communication with a plurality of userequipments.

BACKGROUND ART

Commercial service of a wideband code division multiple access (W-CDMA)system among so-called third-generation communication systems has beenoffered in Japan since 2001. In addition, high speed downlink packetaccess (HSDPA) service for achieving higher-speed data transmissionusing a downlink has been offered by adding a channel for packettransmission (high speed-downlink shared channel (HS-DSCH)) to thedownlink (dedicated data channel, dedicated control channel). Further,in order to increase the speed of data transmission in an uplinkdirection, service of a high speed uplink packet access (HSUPA) systemhas been offered. W-CDMA is a communication system defined by the 3rdgeneration partnership project (3GPP) that is the standard organizationregarding the mobile communication system, where the specifications ofRelease 8 version are produced.

Further, 3GPP is studying new communication systems referred to as longterm evolution (LTE) regarding radio areas and system architectureevolution (SAE) regarding the overall system configuration including acore network (merely referred to as network as well) as communicationsystems independent of W-CDMA.

In the LTE, an access scheme, a radio channel configuration and aprotocol are totally different from those of the current W-CDMA(HSDPA/HSUPA). For example, as to the access scheme, code divisionmultiple access is used in the W-CDMA, whereas in the LTE, orthogonalfrequency division multiplexing (OFDM) is used in a downlink directionand single career frequency division multiple access (SC-FDMA) is usedin an uplink direction. In addition, the bandwidth is 5 MHz in theW-CDMA, while in the LTE, the bandwidth can be selected from 1.4 MHz, 3MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz for each base station. Further,differently from the W-CDMA, circuit switching is not provided but apacket communication system is only provided in the LTE.

The LTE is defined as a radio access network independent of the W-CDMAnetwork because its communication system is configured with a new corenetwork different from a core network (general packet radio service:GPRS) of the W-CDMA. Therefore, for differentiation from the W-CDMAcommunication system, a base station that communicates with a userequipment (UE) and a radio network controller that transmits/receivescontrol data and user data to/from a plurality of base stations arereferred to as an E-UTRAN NodeB (eNB) and an evolved packet core (EPC)or access gateway (aGW), respectively, in the LTE communication system.Unicast service and evolved multimedia broadcast multicast service(E-MBMS service) are provided in this LTE communication system. TheE-MBMS service is broadcast multimedia service, which is merely referredto as MBMS in some cases. Bulk broadcast contents such as news, weatherforecast and mobile broadcast are transmitted to a plurality of userequipments. This is also referred to as point to multipoint service.

Non-Patent Document 1 (Chapter 4.6.1) describes the current decisions by3GPP regarding an overall architecture in the LTE system. The overallarchitecture is described with reference to FIG. 1 . FIG. 1 is a diagramillustrating the configuration of the LTE communication system. Withreference to FIG. 1 , the evolved universal terrestrial radio access(E-UTRAN) is composed of one or a plurality of base stations 102,provided that a control protocol for a user equipment 101 such as aradio resource control (RRC) and user planes such as a packet dataconvergence protocol (PDCP), radio link control (RLC), medium accesscontrol (MAC) and physical layer (PHY) are terminated in the basestation 102.

The base stations 102 perform scheduling and transmission of pagingsignal (also referred to as paging messages) notified from a mobilitymanagement entity (MME) 103. The base stations 102 are connected to eachother by means of an X2 interface. In addition, the base stations 102are connected to an evolved packet core (EPC) by means of an S1interface. More specifically, the base station 102 is connected to themobility management entity (MME) 103 by means of an S1_MME interface andconnected to a serving gateway (S-GW) 104 by means of an S1_U interface.

The MME 103 distributes the paging signal to a plurality of or a singlebase station 102. In addition, the MME 103 performs mobility control ofan idle state. When the user equipment is in the idle state and anactive state, the MME 103 manages a list of tracking areas.

The S-GW 104 transmits/receives user data to/from one or a plurality ofbase stations 102. The S-GW 104 serves as a local mobility anchor pointin handover between base stations. Moreover, a PDN gateway (P-GW) isprovided in the EPC, which performs per-user packet filtering and UE-IDaddress allocation.

The control protocol RRC between the user equipment 101 and the basestation 102 performs broadcast, paging, RRC connection management andthe like. The states of the base station and the user equipment in RRCare classified into RRC_Idle and RRC_CONNECTED. In RRC_IDLE, public landmobile network (PLMN) selection, system information (SI) broadcast,paging, cell reselection, mobility and the like are performed. InRRC_CONNECTED, the user equipment has RRC connection, is capable oftransmitting/receiving data to/from a network, and performs, forexample, handover (HO) and measurement of a neighbor cell.

The current decisions by 3GPP regarding the frame configuration in theLTE system described in Non-Patent Document 1 (Chapter 5) are describedwith reference to FIG. 2 . FIG. 2 is a diagram illustrating theconfiguration of a radio frame used in the LTE communication system.With reference to FIG. 2 , one radio frame is 10 ms. The radio frame isdivided into ten equally sized subframes. The subframe is divided intotwo equally sized slots. The first and sixth subframes contain adownlink synchronization signal (SS) per each radio frame. Thesynchronization signals are classified into a primary synchronizationsignal (P-SS) and a secondary synchronization signal (S-SS).Multiplexing of channels for multimedia broadcast multicast servicesingle frequency network (MBSFN) and for non-MBSFN is performed on aper-subframe basis. Hereinafter, a subframe for MBSFN transmission isreferred to as an MBSFN subframe.

Non-Patent Document 2 describes a signaling example when MBSFN subframesare allocated. FIG. 3 is a diagram illustrating the configuration of theMBSFN frame. With reference to FIG. 3 , the MBSFN subframes areallocated for each MBSFN frame. An MBSFN frame cluster is scheduled. Arepetition period of the MBSFN frame cluster is allocated.

Non-Patent Document 1 (Chapter 5) describes the current decisions by3GPP regarding the channel configuration in the LTE system. It isassumed that the same channel configuration is used in a closedsubscriber group cell (CSG cell) as that of a non-CSG cell. A physicalchannel is described with reference to FIG. 4 . FIG. 4 is a diagramillustrating physical channels used in the LTE communication system.With reference to FIG. 4 , a physical broadcast channel (PBCH) 401 is adownlink channel transmitted from the base station 102 to the userequipment 101. A BCH transport block is mapped to four subframes withina 40 ms interval. There is no explicit signaling indicating 40 mstiming. A physical control format indicator channel (PCFICH) 402 istransmitted from the base station 102 to the user equipment 101. ThePCFICH notifies the number of OFDM symbols used for PDCCHs from the basestation 102 to the user equipment 101. The PCFICH is transmitted in eachsubframe.

A physical downlink control channel (PDCCH) 403 is a downlink channeltransmitted from the base station 102 to the user equipment 101. ThePDCCH notifies the resource allocation, HARQ information related toDL-SCH (downlink shared channel that is one of the transport channelsshown in FIG. 5 described below) and the PCH (paging channel that is oneof the transport channels shown in FIG. 5 ). The PDCCH carries an uplinkscheduling grant. The PDCCH carries acknowledgement (Ack)/negativeacknowledgement (Nack) that is a response signal to uplink transmission.The PDCCH is referred to as an L1/L2 control signal as well.

A physical downlink shared channel (PDSCH) 404 is a downlink channeltransmitted from the base station 102 to the user equipment 101. ADL-SCH (downlink shared channel) that is a transport channel and a PCHthat is a transport channel are mapped to the PDSCH. A physicalmulticast channel (PMCH) 405 is a downlink channel transmitted from thebase station 102 to the user equipment 101. A multicast channel (MCH)that is a transport channel is mapped to the PMCH.

A physical uplink control channel (PUCCH) 406 is an uplink channeltransmitted from the user equipment 101 to the base station 102. ThePUCCH carries Ack/Nack that is a response signal to downlinktransmission. The PUCCH carries a channel quality indicator (CQI)report. The CQI is quality information indicating the quality ofreceived data or channel quality. In addition, the PUCCH carries ascheduling request (SR). A physical uplink shared channel (PUSCH) 407 isan uplink channel transmitted from the user equipment 101 to the basestation 102. A UL-SCH (uplink shared channel that is one of thetransport channels shown in FIG. 5 ) is mapped to the PUSCH.

A physical hybrid ARQ indicator channel (PHICH) 408 is a downlinkchannel transmitted from the base station 102 to the user equipment 101.The PHICH carries Ack/Nack that is a response to uplink transmission. Aphysical random access channel (PRACH) 409 is an uplink channeltransmitted from the user equipment 101 to the base station 102. ThePRACH carries a random access preamble.

A downlink reference signal which is a known symbol in a mobilecommunication system is inserted in the first, third and last OFDMsymbols of each slot. The physical layer measurement objects of a userequipment include reference symbol received power (RSRP).

The transport channel described in Non-Patent Document 1 (Chapter 5) isdescribed with reference to FIG. 5 . FIG. 5 is a diagram illustratingtransport channels used in the LTE communication system. Part (A) ofFIG. 5 shows mapping between a downlink transport channel and a downlinkphysical channel. Part (B) of FIG. 5 shows mapping between an uplinktransport channel and an uplink physical channel. A broadcast channel(BCH) is broadcast to the entire base station (cell) regarding thedownlink transport channel. The BCH is mapped to the physical broadcastchannel (PBCH).

Retransmission control according to a hybrid ARQ (HARD) is applied to adownlink shared channel (DL-SCH). The DL-SCH enables broadcast to theentire base station (cell). The DL-SCH supports dynamic or semi-staticresource allocation. The semi-static resource allocation is alsoreferred to as persistent scheduling. The DL-SCH supports discontinuousreception (DRX) of a user equipment for enabling the user equipment tosave power. The DL-SCH is mapped to the physical downlink shared channel(PDSCH).

The paging channel (PCH) supports DRX of the user equipment for enablingthe user equipment to save power. Broadcast to the entire base station(cell) is required for the PCH. The PCH is mapped to physical resourcessuch as the physical downlink shared channel (PDSCH) that can be useddynamically for traffic or physical resources such as the physicaldownlink control channel (PDCCH) of the other control channel. Themulticast channel (MCH) is used for broadcast to the entire base station(cell). The MCH supports SFN combining of MBMS service (MTCH and MCCH)in multi-cell transmission. The MCH supports semi-static resourceallocation. The MCH is mapped to the PMCH.

Retransmission control according to a hybrid ARQ (HARQ) is applied to anuplink shared channel (UL-SCH). The UL-SCH supports dynamic orsemi-static resource allocation. The UL-SCH is mapped to the physicaluplink shared channel (PUSCH). A random access channel (RACH) shown inpart (B) of FIG. 5 is limited to control information. The RACH involvesa collision risk. The RACH is mapped to the physical random accesschannel (PRACH).

The HARQ is described. The HARQ is the technique for improving thecommunication quality of a channel by combination of automatic repeatrequest and forward error correction. The HARQ has an advantage thaterror correction functions effectively by retransmission even for achannel whose communication quality changes. In particular, it is alsopossible to achieve further quality improvement in retransmissionthrough combination of the reception results of the first transmissionand the reception results of the retransmission.

An example of the retransmission method is described. In a case wherethe receiver fails to successfully decode the received data, in otherwords, in a case where a cyclic redundancy check (CRC) error occurs(CRC=NG), the receiver transmits “Nack” to the transmitter. Thetransmitter that has received “Nack” retransmits the data. In a casewhere the receiver successfully decodes the received data, in otherwords, in a case where a CRC error does not occur (CRC=OK), the receivertransmits “AcK” to the transmitter. The transmitter that has received“Ack” transmits the next data.

Examples of the HARQ system include chase combining. In chase combining,the same data sequence is transmitted in the first transmission andretransmission, which is the system for improving gains by combining thedata sequence of the first transmission and the data sequence of theretransmission in retransmission. This is based on the idea that correctdata is partially included even if the data of the first transmissioncontains an error, and highly accurate data transmission is enabled bycombining the correct portions of the first transmission data and theretransmission data. Another example of the HARQ system is incrementalredundancy (IR). The IR is aimed to increase redundancy, where a paritybit is transmitted in retransmission to increase the redundancy bycombining the first transmission and retransmission, to thereby improvethe quality by an error correction function.

A logical channel (hereinafter, referred to as “logical channel” in somecases) described in Non-Patent Document 1 (Chapter 6) is described withreference to FIG. 6 . FIG. 6 is a diagram illustrating logical channelsused in an LTE communication system. Part (A) of FIG. 6 shows mappingbetween a downlink logical channel and a downlink transport channel.Part (B) of FIG. 6 shows mapping between an uplink logical channel andan uplink transport channel. A broadcast control channel (BCCH) is adownlink channel for broadcast system control information. The BCCH thatis a logical channel is mapped to the broadcast channel (BCH) ordownlink shared channel (DL-SCH) that is a transport channel.

A paging control channel (PCCH) is a downlink channel for transmittingpaging signals. The PCCH is used when the network does not know the celllocation of a user equipment. The PCCH that is a logical channel ismapped to the paging channel (PCH) that is a transport channel. A commoncontrol channel (CCCH) is a channel for transmission control informationbetween user equipments and a base station. The CCCH is used in a casewhere the user equipments have no RRC connection with the network. In adownlink direction, the CCCH is mapped to the downlink shared channel(DL-SCH) that is a transport channel. In an uplink direction, the CCCHis mapped to the uplink shared channel (UL-SCH) that is a transportchannel.

A multicast control channel (MCCH) is a downlink channel forpoint-to-multipoint transmission. The MCCH is used for transmission ofMBMS control information for one or several MTCHs from a network to auser equipment. The MCCH is used only by a user equipment duringreception of the MBMS. The MCCH is mapped to the downlink shared channel(DL-SCH) or multicast channel (MCH) that is a transport channel.

A dedicated control channel (DCCH) is a channel that transmits dedicatedcontrol information between a user equipment and a network. The DCCH ismapped to the uplink shared channel (UL-SCH) in uplink and mapped to thedownlink shared channel (DL-SCH) in downlink.

A dedicated traffic channel (DTCH) is a point-to-point communicationchannel for transmission of user information to a dedicated userequipment. The DTCH exists in uplink as well as downlink. The DTCH ismapped to the uplink shared channel (UL-SCH) in uplink and mapped to thedownlink shared channel (DL-SCH) in downlink.

A multicast traffic channel (MTCH) is a downlink channel for trafficdata transmission from a network to a user equipment. The MTCH is achannel used only by a user equipment during reception of the MBMS. TheMTCH is mapped to the downlink shared channel (DL-SCH) or multicastchannel (MCH).

GCI represents a global cell identity. A closed subscriber group cell(CSG cell) is introduced in the LTE and universal mobiletelecommunication system (UMTS). The CSG is described below (see Chapter3.1 of Non-Patent Document 3). The closed subscriber group (CSG) is acell (cell for specific subscribers) in which subscribers who areallowed to use are specified by an operator. The specified subscribersare allowed to access one or more E-UTRAN cells of a public land mobilenetwork (PLMN). One or more E-UTRAN cells in which the specifiedsubscribers are allowed access are referred to as “CSG cell(s)”. Notethat access is limited in the PLMN. The CSG cell is part of the PLMNthat broadcasts a specific CSG identity (CSG ID; CSG-ID). The authorizedmembers of the subscriber group who have registered in advance accessthe CSG cells using the CSG-ID that is the access permissioninformation.

The CSG-ID is broadcast by the CSG cell or cells. A plurality of CSG-IDsexist in a mobile communication system. The CSG-IDs are used by userequipments (UEs) for making access from CSG-related members easier. Thelocations of user equipments are traced based on an area composed of oneor more cells. The locations are traced for enabling tracing of thelocations of user equipments and calling (calling of user equipments)even in an idle state. An area for tracing locations of user equipmentsis referred to as a tracking area. A CSG whitelist is a list stored in auniversal subscriber identity module (USIM) in which all CSG IDs of theCSG cells to which the subscribers belong are recorded. The CSGwhitelist is also referred to as an allowed CSG ID list in some cases.

A “suitable cell” is described below (see Chapter 4.3 of Non-PatentDocument 3). The “suitable cell” is a cell on which a UE camps to obtainnormal service. Such a cell shall fulfill the following conditions.

(1) The cell is part of the selected PLMN or the registered PLMN, orpart of the PLMN of an “equivalent PLMN list”.

(2) According to the latest information provided by a non-access stratum(NAS), the cell shall further fulfill the following conditions:

(a) the cell is not a barred cell;

(b) the cell is part of at least one tracking area (TA), not part of thelist of “forbidden LAs for roaming”, where the cell needs to fulfill (1)above;

(c) the cell shall fulfill the cell selection criteria; and

(d) for a cell specified as CSG cell by system information (SI), theCSG-ID is part of a “CSG whitelist” of the UE (contained in the CSGwhitelist of the UE).

An “acceptable cell” is described below (see Chapter 4.3 of Non-PatentDocument 3). This is the cell on which a UE camps to obtain limitedservice (emergency calls). Such a cell shall fulfill all the followingrequirements. That is, the minimum required set for initiating anemergency call in an E-UTRAN network are as follows: (1) the cell is nota barred cell; and (2) the cell fulfills the cell selection criteria.

Camping on a cell represents the state where a UE has completed the cellselection/reselection process and the UE has selected a cell formonitoring the system information and paging information.

3GPP is studying base stations referred to as Home-NodeB (Home-NB; HNB)and Home-eNodeB (Home-eNB; HeNB). HNB/HeNB is a base station for, forexample, household, corporation or commercial access service inUTRAN/E-UTRAN. Non-Patent Document 4 discloses three different modes ofthe access to the HeNB and HNB. Specifically, those are an open accessmode, a closed access mode and a hybrid access mode.

The respective modes have the following characteristics. In the openaccess mode, the HeNB and HNB are operated as a normal cell of a normaloperator. In the closed access mode, the HeNB and HNB are operated as aCSG cell. The CSG cell is a cell where only CSG members are allowedaccess. In the hybrid access mode, non-CSG members are allowed access atthe same time. In other words, a cell in the hybrid access mode (alsoreferred to as hybrid cell) is the cell that supports both the openaccess mode and the closed access mode.

3GPP discusses that all physical cell identities (PCIs) are split(referred to as PCI-split) into ones reserved for CSG cells and theothers reserved for non-CSG cells (see Non-Patent Document 5). Further,3GPP discusses that the PCI split information is broadcast in the systeminformation from the base station to the user equipments being servedthereby. Non-Patent Document 5 discloses the basic operation of a userequipment using PCI split. The user equipment that does not have the PCIsplit information needs to perform cell search using all PCIs (forexample, using all 504 codes). On the other hand, the user equipmentthat has the PCI split information is capable of performing cell searchusing the PCI split information.

Further, 3GPP is pursuing specifications standard of long term evolutionadvanced (LTE-A) as Release 10 (see Non-Patent Document 6 and Non-PatentDocument 7).

As to the LTE-A system, it is studied that a relay (relay node (RN)) issupported for achieving a high data rate, high cell-edge throughput, newcoverage area or the like. The relay node is wirelessly connected to theradio-access network via a donor cell (Donor eNB; DeNB). The network(NW)-to-relay node link shares the same frequency band with thenetwork-to-UE link within the range of the donor cell. In this case, theUE in the specifications of Release 8 can also be connected to the donorcell. The link between a donor cell and a relay node is referred to as abackhaul link, and the link between the relay node and the UE isreferred to as an access link.

As the method of multiplexing backhaul links in frequency divisionduplex (FDD), the transmission from DeNB to RN is done in the downlink(DL) frequency band, whereas the transmission from RN to DeNB is done inthe uplink (UL) frequency band. As the method of partitioning resourcesat the relay, the link from DeNB to RN and the link from RN to UE aretime division multiplexed in a single frequency band, and the link fromRN to DeNB and the link from UE to RN are time division multiplexed in asingle frequency band as well. This prevents, in the relay node, thetransmission of the relay node from causing interference to thereception of its own relay node.

3GPP studies not only normal eNBs (macro cells) but also so-called localnodes such as pico eNB (pico cell), HeNB/HNB/CSG cell, node for hotzonecells, relay node and remote radio head (RRH).

Those local nodes are deployed for implementing macro cells uponrequests for various types of service such as high-speed andhigh-capacity communication. For example, it is required to deploy alarge number of HeNBs in shopping malls, apartment buildings, schools,and companies. This leads to a case where the HeNB is deployed in thecoverage of a macro cell. In the case where the HeNB is deployed in thecoverage of a macro cell, interference occurs between the macro cell orHeNB and a user equipment (UE). Such interference hinders thecommunication between the user equipment (UE) and the macro cell orHeNB, which decreases the communication rate. If the interference powerbecomes larger, communication cannot be made. This requires the methodfor avoiding the interference occurring in a situation in which a macrocell and a local node are deployed to coexist, to thereby optimize thecommunication quality.

As a method of reducing the interference between a macro cell and aHeNB, there is a method of notifying a HeNB of the information relatedto the interference to a physical resource used by a macro cell(hereinafter, referred to as “interference-related information in somecases). Non-Patent Document 8 discloses the method of notifying, by amacro cell, a HeNB of the high interference indication (HII) andoverload indicator (01) as the interference-related information. Inaddition, Non-Patent Document 9 discloses that a macro cell notifies aHeNB of the HIT via a UE being served by the macro cell.

PRIOR ART DOCUMENTS Non-Patent Documents

-   Non-Patent Document 1: 3GPP TS36.300 V9.1.0 Chapter 4.6.1, Chapter    4.6.2, Chapter 5, Chapter 6, Chapter 10.1.2 and Chapter 10.7-   Non-Patent Document 2: 3GPP R1-072963-   Non-Patent Document 3: 3GPP TS36.304 V9.0.0 Chapter 3.1, Chapter 4.3    and Chapter 5.2.4-   Non-Patent Document 4: 3GPP S1-083461-   Non-Patent Document 5: 3GPP R2-082899-   Non-Patent Document 6: 3GPP TR36.814 V1.1.1-   Non-Patent Document 7: 3GPP TR36.912 V9.0.0-   Non-Patent Document 8: 3GPP R4-093203-   Non-Patent Document 9: 3GPP R1-094839

SUMMARY OF INVENTION Problem to be Solved by the Invention

Non-Patent Document 8 describes that an X2 interface is provided betweena macro cell and a HeNB, between a macro cell and a HeNBGW, and betweena HeNBGW and a HeNB, and the macro cell notifies the HeNB of the HII andOI by means of the X2 interface. However, the HeNB is also assumed to beused at home, and further, it is studied to deploy the HeNB so as to bemanaged by a general user not by an operator. When a HeNB is deployed soas not to be managed by an operator as described above, a problem thatthe configuration becomes complicated occurs if the HeNBs and the macrocell and the HeNB are connected to each other by means of the X2interface.

Non-Patent Document 9 describes the channel on which notification ismade from a UE to a HeNB but does not describe anything else, and themechanism in which a macro cell notifies a HeNB of the HII is unclear.

An object of the present invention is to provide a mobile communicationsystem capable of easily notifying the interference-related informationand avoiding interference in a situation in which a base station devicehaving a relatively large coverage such as a macro cell and a basestation device having a relatively small coverage such as a local nodeare deployed to coexist.

Means to Solve the Problem

A mobile communication system according to the present inventionincludes a plurality of base station devices and a user equipment deviceconfigured to perform radio communication with each of the base stationdevices, wherein: the plurality of base station devices include alarge-scale base station device having a large-scale coverage that isrelatively large and a small-scale base station device having asmall-scale coverage that is relatively small, as a coverage in a rangein which communication with the user equipment device is made; and thelarge-scale base station device notifies, via the user equipment devicepresent in the large-scale coverage, the small-scale base station devicepresent in the large-scale coverage of interference-related informationrelated to interference to a physical resource to be used.

Effects of the Invention

According to the mobile communication system of the present invention,the mobile communication system includes a large-scale base stationdevice having a large-scale coverage, a small-scale base station devicehaving a small-scale coverage, and a user equipment device. Thelarge-scale base station device notifies, via the user equipment devicepresent in the large-scale coverage, the small-scale base station devicepresent in the large-scale coverage of the interference-relatedinformation. This enables to easily notify the small-scale base stationdevice of the interference-related information, which avoidsinterference in the mobile communication system and enables to prevent adecrease in communication rate and interruption of communication.Therefore, it is possible to avoid interference and achieve goodcommunication quality even in a situation in which a large number oflarge-scale base station devices and small-scale base station devicesare deployed in a complicated manner.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the configuration of an LTEcommunication system.

FIG. 2 is a diagram illustrating the configuration of a radio frame usedin the LTE communication system.

FIG. 3 is a diagram illustrating the configuration of an MBSFN frame.

FIG. 4 is a diagram illustrating physical channels used in the LTEcommunication system.

FIG. 5 is a diagram illustrating transport channels used in the LTEcommunication system.

FIG. 6 is a diagram illustrating logical channels used in the LTEcommunication system.

FIG. 7 is a block diagram showing the overall configuration of an LTEmobile communication system currently under discussion of 3GPP.

FIG. 8 is a block diagram showing the configuration of a user equipment(user equipment 71 of FIG. 7 ) according to the present invention.

FIG. 9 is a block diagram showing the configuration of a base station(base station 72 of FIG. 7 ) according to the present invention.

FIG. 10 is a block diagram showing the configuration of an MME (MME unit73 of FIG. 7 ) according to the present invention.

FIG. 11 is a block diagram showing the configuration of a HeNBGW 74shown in FIG. 7 that is a HeNBGW according to the present invention.

FIG. 12 is a flowchart showing an outline from a cell search to an idlestate operation performed by a user equipment (UE) in the LTEcommunication system.

FIG. 13 is a conceptual diagram in a case where HeNBs are deployed inthe coverage of a macro cell.

FIG. 14 is a diagram showing a sequence example of a mobilecommunication system in a case where a macro cell judges a HeNB deployedin the coverage.

FIG. 15 is a diagram showing a sequence example of a mobilecommunication system in a case of judging whether or not a HeNB isdeployed in the coverage of the macro cell.

FIG. 16 is a conceptual diagram in a case where only one HeNB isdeployed in the coverage of the macro cell and a plurality of UEs arepresent in the coverage of the macro cell.

FIG. 17 is a diagram showing a sequence example of a mobilecommunication system in a case where the HII is notified via a UE havingthe largest received power from a HeNB.

FIG. 18 is a conceptual diagram showing a case where HeNBs are deployedin the coverage of the macro cell.

FIG. 19 is a diagram showing a sequence example of a part of a mobilecommunication system in a case of judging a HeNB deployed in a specificreceived power range.

FIG. 20 is a conceptual diagram in a case where HeNBs are deployed inthe coverage of the macro cell.

FIG. 21 is a diagram showing a sequence example of a part of a mobilecommunication system in a case where the HII is notified via a UEpresent in a specific received power range from a HeNB.

FIG. 22 is a conceptual diagram in a case where a UE notifies a HeNB ofthe HII with the RACH configuration of the HeNB.

FIG. 23 is a conceptual diagram in a case where a UE obtains a RACHconfiguration parameter from a HeNB present in its vicinity.

FIG. 24 is a diagram showing a sequence example of a mobilecommunication system in a case where the UE changes to RRC_Idle and thennotifies a HeNB of the HII.

FIG. 25 is a diagram showing a sequence example of a mobilecommunication system in a case where a UE notifies a HeNB of the HIIwhile remaining in an RRC connected state.

FIG. 26 is a diagram showing a sequence example of a mobilecommunication system in a case where a timer is provided for releasingscheduling for avoiding interference by a HeNB.

FIG. 27 is a diagram showing a sequence example of a mobilecommunication system in a case where scheduling for avoidinginterference is released by a HeNB upon reception of an HII releasesignal.

FIG. 28 is a conceptual diagram in a case where a UE notifies a HeNB ofthe HII with a RACH configuration of a serving cell.

EMBODIMENTS FOR CARRYING OUT THE INVENTION First Embodiment

FIG. 7 is a block diagram showing an overall configuration of an LTEmobile communication system, which is currently under discussion of3GPP. Currently, 3GPP is studying an overall system configurationincluding closed subscriber group (CSG) cells (Home-eNodeBs (Home-eNB;HeNB) of E-UTRAN, Home-NB (HNB) of UTRAN) and non-CSG cells (eNodeB(eNB) of E-UTRAN, NodeB (NB) of UTRAN, and BSS of GERAN) and, as toE-UTRAN, is proposing the configuration as shown in FIG. 7 (see Chapter4.6.1 of Non-Patent Document 1).

FIG. 7 is described. A user equipment device (hereinafter, referred toas “user equipment” or “UE”) 71 is capable of performing radiocommunication with a base station device (hereinafter, referred to as“base station”) 72 and transmits/receives signals through radiocommunication. The base stations 72 are classified into an eNB 72-1 thatis a macro cell and a Home-eNB 72-2 that is a local node. The eNB 72-1corresponds to a large-scale base station device and has a relativelylarge-scale coverage as the coverage in a range in which communicationis allowed with the user equipment UE 71. The Home-eNB 72-2 correspondsto a small-scale base station device and has a relatively small-scalecoverage as the coverage.

The eNB 72-1 is connected to an MME/S-GW unit (hereinafter, referred toas an “MME unit” in some cases) 73 including an MME, S-GW or MME andS-GW through an S1 interface, and control information is communicatedbetween the eNB 72-1 and the MME unit 73. A plurality of MME units 73may be connected to one eNB 72-1. The eNBs 72-1 are connected to eachother by means of an X2 interface, and control information iscommunicated between the eNBs 72-1.

The Home-eNB 72-2 is connected to the MME unit 73 by means of an S1interface, and control information is communicated between the Home-eNB72-2 and the MME unit 73. A plurality of Home-eNBs 72-2 are connected toone MME unit 73. While, the Home-eNBs 72-2 are connected to the MMEunits 73 through a Home-eNB Gateway (HeNBGW) 74. The Home-eNBs 72-2 areconnected to the HeNBGW 74 by means of the S1 interface, and the HeNBGW74 is connected to the MME units 73 through an S1 interface. One or aplurality of Home-eNBs 72-2 are connected to one HeNBGW 74, andinformation is communicated therebetween through an S1 interface. TheHeNBGW 74 is connected to one or a plurality of MME units 73, andinformation is communicated therebetween through an S1 interface.

Further, 3GPP is currently studying the configuration below. The X2interface between the Home-eNBs 72-2 is not supported. The HeNBGW 74appears to the MME unit 73 as the eNB 72-1. The HeNBGW 74 appears to theHome-eNB 72-2 as the MME unit 73. The interfaces between the Home-eNBs72-2 and the MME units 73 are the same, which are the S1 interfaces,irrespective of whether or not the Home-eNB 72-2 is connected to the MMEunit 73 through the HeNBGW 74. The mobility to the Home-eNB 72-2 or themobility from the Home-eNB 72-2 that spans the plurality of MME units 73is not supported. The Home-eNB 72-2 supports a single cell.

FIG. 8 is a block diagram showing the configuration of the userequipment (user equipment 71 of FIG. 7 ) according to the presentinvention. The transmission process of the user equipment 71 shown inFIG. 8 is described. First, a transmission data buffer unit 803 storesthe control data from a protocol processing unit 801 and the user datafrom an application unit 802. The data stored in the transmission databuffer unit 803 is transmitted to an encoding unit 804 and is subjectedto encoding process such as error correction. There may exist the dataoutput from the transmission data buffer unit 803 directly to amodulating unit 805 without encoding process. The data encoded by theencoding unit 804 is modulated by the modulating unit 805. The modulateddata is output to a frequency converting unit 806 after being convertedinto a baseband signal, and then is converted into a radio transmissionfrequency. After that, a transmission signal is transmitted from anantenna 807 to the base station 72.

The user equipment 71 executes the reception process as follows. Theantenna 807 receives the radio signal from the base station 72. Thereceived signal is converted from a radio reception frequency to abaseband signal by the frequency converting unit 806 and is thendemodulated by a demodulating unit 808. The demodulated data istransmitted to a decoding unit 809 and is subjected to decoding processsuch as error correction. Among the pieces of decoded data, the controldata is transmitted to the protocol processing unit 801, while the userdata is transmitted to the application unit 802. A series of processesof the user equipment 71 is controlled by a control unit 810. This meansthat, though not shown in FIG. 8 , the control unit 810 is connected tothe respective units 801 to 809.

FIG. 9 is a block diagram showing the configuration of the base station(base station 72 of FIG. 7 ) according to the present invention. Thetransmission process of the base station 72 shown in FIG. 9 isdescribed. An EPC communication unit 901 performs datatransmission/reception between the base station 72 and the EPCs (such asMME unit 73 and HeNBGW 74). A communication with another base stationunit 902 performs data transmission/reception to/from another basestation. The X2 interface between the Home-eNBs 72-2 is not intended tobe supported, and accordingly, it is conceivable that the communicationwith another base station unit 902 may not exist in the Home-eNB 72-2.The EPC communication unit 901 and the communication with another basestation unit 902 respectively transmit/receive information to/from aprotocol processing unit 903. The control data from the protocolprocessing unit 903, and the user data and control data from the EPCcommunication unit 901 and the communication with another base stationunit 902 are stored in a transmission data buffer unit 904.

The data stored in the transmission data buffer unit 904 is transmittedto an encoding unit 905 and is then subjected to encoding process suchas error correction. There may exist the data output from thetransmission data buffer unit 904 directly to a modulating unit 906without encoding process. The encoded data is modulated by themodulating unit 906. The modulated data is output to a frequencyconverting unit 907 after being converted into a baseband signal, and isthen converted into a radio transmission frequency. After that, atransmission signal is transmitted from an antenna 908 to one or aplurality of user equipments 71.

While, the reception process of the base station 72 is executed asfollows. A radio signal from one or a plurality of user equipments 71 isreceived by the antenna 908. The received signal is converted from aradio reception frequency into a baseband signal by the frequencyconverting unit 907, and is then demodulated by a demodulating unit 909.The demodulated data is transmitted to a decoding unit 910 and is thensubjected to decoding process such as error correction. Among the piecesof decoded data, the control data is transmitted to the protocolprocessing unit 903, EPC communication unit 901, or communication withanother base station unit 902, while the user data is transmitted to theEPC communication unit 901 and communication with another base stationunit 902. A series of processes by the base station 72 is controlled bya control unit 911. This means that, though not shown in FIG. 9 , thecontrol unit 911 is connected to the respective units 901 to 910.

The functions of the Home-eNB 72-2 currently under discussion of 3GPPare described below (see Chapter 4.6.2 of Non-Patent Document 1). TheHome-eNB 72-2 has the same function as that of the eNB 72-1. Inaddition, the Home-eNB 72-2 has the function of discovering a suitableserving HeNBGW 74 in a case of connection to the HeNBGW 74. The Home-eNB72-2 is connected only to one HeNBGW 74. That is, in a case of theconnection to the HeNBGW 74, the Home-eNB 72-2 does not use the Flexfunction in the S1 interface. When the Home-eNB 72-2 is connected to oneHeNBGW 74, it is not simultaneously connected to another HeNBGW 74 oranother MME unit 73.

The TAC and PLMN ID of the Home-eNB 72-2 are supported by the HeNBGW 74.When the Home-eNB 72-2 is connected to the HeNBGW 74, selection of theMME unit 73 at “UE attachment” is performed by the HeNBGW 74 instead ofthe Home-eNB 72-2. The Home-eNB 72-2 may be deployed without networkplanning. In this case, the Home-eNB 72-2 is moved from one geographicalarea to another geographical area. Accordingly, the Home-eNB 72-2 inthis case is required to be connected to a different HeNBGW 74 dependingon its location.

FIG. 10 is a block diagram showing the configuration of the MME (MMEunit 73 of FIG. 7 ) according to the present invention. A PDN GWcommunication unit 1001 performs data transmission/reception between theMME unit 73 and a PDN GW. A base station communication unit 1002performs data transmission/reception between the MME unit 73 and thebase station 72 by means of the S1 interface. In the case where the datareceived from the PDN GW is user data, the user data is transmitted fromthe PDN GW communication unit 1001 to the base station communicationunit 1002 through a user plane communication unit 1003 and is thentransmitted to one or a plurality of base stations 72. In the case wherethe data received from the base station 72 is user data, the user datais transmitted from the base station communication unit 1002 to the PDNGW communication unit 1001 through the user plane communication unit1003 and is then transmitted to the PDN GW.

In the case where the data received from the PDN GW is control data, thecontrol data is transmitted from the PDN GW communication unit 1001 to acontrol plane control unit 1005. In the case where the data receivedfrom the base station 72 is control data, the control data istransmitted from the base station communication unit 1002 to the controlplane control unit 1005.

A HeNBGW communication unit 1004 is provided in the case where theHeNBGW 74 is provided, which performs data transmission/reception bymeans of the interface (IF) between the MME unit 73 and the HeNBGW 74according to an information type. The control data received from theHeNBGW communication unit 1004 is transmitted from the HeNBGWcommunication unit 1004 to the control plane control unit 1005. Theprocessing results of the control plane control unit 1005 aretransmitted to the PDN GW through the PDN GW communication unit 1001.The processing results of the control plane control unit 1005 aretransmitted to one or a plurality of base stations 72 by means of the S1interface through the base station communication unit 1002, and aretransmitted to one or a plurality of HeNBGWs 74 through the HeNBGWcommunication unit 1004.

The control plane control unit 1005 includes a NAS security unit 1005-1,an SAE bearer control unit 1005-2 and an idle state mobility managingunit 1005-3, and performs overall process for the control plane. The NASsecurity unit 1005-1 provides, for example, security of a non-accessstratum (NAS) message. The SAE bearer control unit 1005-2 manages, forexample, a system architecture evolution (SAE) bearer. The idle statemobility managing unit 1005-3 performs, for example, mobility managementof an idle state (LTE-IDLE state, which is merely referred to as idle aswell), generation and control of paging signal in an idle state,addition, deletion, update and search of a tracking area (TA) of one ora plurality of user equipments 71 being served thereby, and TA listmanagement.

The MME unit 73 begins a paging protocol by transmitting a pagingmessage to the cell belonging to a tracking area (TA) in which the UE isregistered. The idle state mobility managing unit 1005-3 may manage theCSG of the Home-eNBs 72-2 to be connected to the MME unit 73, CSG-IDsand a whitelist.

In the CSG-ID management, the relationship between a user equipmentcorresponding to the CSG-ID and the CSG cell is managed (added, deleted,updated or searched). For example, it may be the relationship betweenone or a plurality of user equipments whose user access registration hasbeen performed with a CSG-ID and the CSG cells belonging to this CSG-ID.In the whitelist management, the relationship between the user equipmentand the CSG-ID is managed (added, deleted, updated or searched). Forexample, one or a plurality of CSG-IDs with which user registration hasbeen performed by a user equipment may be stored in the whitelist. Theabove-mentioned management related to the CSG may be performed byanother part of the MME unit 73. A series of processes by the MME unit73 is controlled by a control unit 1006. This means that, though notshown in FIG. 10 , the control unit 1006 is connected to the respectiveunits 1001 to 1005.

The function of the MME currently under discussion of 3GPP is describedbelow (see Chapter 4.6.2 of Non-Patent Document 1). The MME performsaccess control for one or a plurality of user equipments being membersof closed subscriber groups (CSGs). The MME recognizes the execution ofpaging optimization as an option.

FIG. 11 is a block diagram showing the configuration of the HeNBGW 74shown in FIG. 7 that is a HeNBGW according to the present invention. AnEPC communication unit 1101 performs data transmission/reception betweenthe HeNBGW 74 and the MME unit 73 by means of the S1 interface. A basestation communication unit 1102 performs data transmission/receptionbetween the HeNBGW 74 and the Home-eNB 72-2 by means of the S1interface. A location processing unit 1103 performs the process oftransmitting, to a plurality of Home-eNBs 72-2, the registrationinformation or the like among the data transmitted from the MME unit 73through the EPC communication unit 1101. The data processed by thelocation processing unit 1103 is transmitted to the base stationcommunication unit 1102 and is transmitted to one or a plurality ofHome-eNBs 72-2 through the S1 interface.

The data only caused to pass through (to be transparent) withoutrequiring the process by the location processing unit 1103 is passedfrom the EPC communication unit 1101 to the base station communicationunit 1102, and is transmitted to one or a plurality of Home-eNBs 72-2through the S1 interface. A series of processes by the HeNBGW 74 iscontrolled by a control unit 1104. This means that, though not shown inFIG. 11 , the control unit 1104 is connected to the respective units1101 to 1103.

The function of the HeNBGW 74 currently under discussion of 3GPP isdescribed below (see Chapter 4.6.2 of Non-Patent Document 1). The HeNBGW74 relays an S1 application. The HeNBGW 74 terminates the S1 applicationthat is not associated with the user equipment 71 though it is a part ofthe procedures toward the Home-eNB 72-2 and towards the MME unit 73.When the HeNBGW 74 is deployed, the procedure that is not associatedwith the user equipment 71 is communicated between the Home-eNB 72-2 andthe HeNBGW 74 and between the HeNBGW 74 and the MME unit 73. The X2interface is not set between the HeNBGW 74 and another node. The HeNBGW74 recognizes the execution of paging optimization as an option.

Next, an example of a typical cell search method in a mobilecommunication system is described. FIG. 12 is a flowchart showing anoutline from cell search to idle state operation performed by a userequipment (UE) in the LTE communication system. When the cell search isstarted by the user equipment, in Step ST1201, the slot timing and frametiming are synchronized by a primary synchronization signal (P-SS) and asecondary synchronization signal (S-SS) transmitted from a nearby basestation. Synchronization codes, which correspond to physical cellidentities (PCIs) assigned per cell one by one, are assigned to thesynchronization signals (SS) including the P-SS and S-SS. The number ofPCIs is currently studied in 504 ways, and these 504 ways are used forsynchronization, and the PCIs of the synchronized cells are detected(specified).

Next, in Step ST1202, a reference signal RS of the synchronized cells,which is transmitted from the base station per cell, is detected and thereceived power is measured. The code corresponding to the PCI one by oneis used for the reference signal RS, and separation from the other cellsis enabled by correlation using the code. The code for RS of the cell isderived from the PCI specified in Step ST1201, which makes it possibleto detect the RS and measure the RS received power.

Next, in Step ST1203, the cell having the best RS reception quality (forexample, cell having the highest RS received power; best cell) isselected from one or more cells that have been detected up to StepST1202.

In Step ST1204, next, the PBCH of the best cell is received, and theBCCH that is the broadcast information is obtained. A master informationblock (MIB) containing the cell configuration information is mapped onthe BCCH over the PBCH. Accordingly, the MIB is obtained by obtainingthe BCCH through reception of the PBCH. Examples of the MIB informationinclude the downlink (DL) system bandwidth (also referred to astransmission bandwidth configuration (dl-bandwidth)), transmissionantenna number and system frame number (SFN).

In Step ST 1205, next, the DL-SCH of the cell is received based on thecell configuration information of the MIB, to thereby obtain a systeminformation block (SIB) 1 of the broadcast information BCCH. The SIB1contains the information regarding access to the cell, informationrelated to cell selection and scheduling information of other SIB (SIBk;k is an integer equal to or larger than two). In addition, the SIB1contains a tracking area code (TAC).

In Step ST1206, next, the user equipment compares the TAC of the SIB1received in Step ST1205 with the TAC that has been already possessed bythe user equipment. In a case where they are identical to each other asa result of comparison, the user equipment enters an idle stateoperation in the cell. In a case where they are different from eachother as a result of comparison, the user equipment requires a corenetwork (EPC) (including MME and the like) to change a TA through thecell for performing tracking area update (TAU). The core network updatesthe TA based on an identification number (such as a UE-ID) of the userequipment transmitted from the user equipment together with a TAUrequest signal. The core network updates the TA, and then transmits theTAU accepted signal to the user equipment. The user equipment rewrites(updates) the TAC (or TAC list) of the user equipment with the TAC ofthe cell. After that, the user equipment enters the idle state operationin the cell.

In the LTE and universal mobile telecommunication system (UMTS), theintroduction of a closed subscriber group (CSG) cell is studied. Asdescribed above, access is allowed for only one or a plurality of userequipments registered with the CSG cell. The CSG cell and one or aplurality of user equipments that have been registered constitute oneCSG. A specific identification number referred to as CSG-ID is added tothe thus constituted CSG. Note that one CSG may contain a plurality ofCSG cells. After being registered with any one of the CSG cells, theuser equipment can access another CSG cell of the CSG to which the CSGcell with which the user equipment has been registered belongs.

Alternatively, the Home-eNB in the LTE or the Home-NB in the UMTS isused as the CSG cell in some cases. The user equipment registered withthe CSG cell has a whitelist. Specifically, the whitelist is stored inthe subscriber identity module (SIM)/USIM. The CSG information of theCSG cell with which the user equipment has been registered is stored inthe whitelist. Specific examples of the CSG information include CSG-ID,tracking area identity (TAI) and TAC. Any one of the CSG-ID and TAC isadequate as long as they are associated with each other. Alternatively,GCI is adequate as long as the CSG-ID and TAC are associated with theglobal cell identity (GCI).

As can be seen from the above, the user equipment that does not have awhitelist (including a case where the whitelist is empty in the presentinvention) is not allowed to access the CSG cell but is allowed toaccess the non-CSG cell only. On the other hand, the user equipmentwhich has a whitelist is allowed to access the CSG cell of the CSG-IDwith which registration has been performed as well as the non-CSG cell.

3GPP discusses that all physical cell identities (PCIs) are split(referred to as PCI-split) into ones reserved for CSG cells and theothers reserved for non-CSG cells (see Non-Patent Document 5). Further,3GPP discusses that the PCI split information is broadcast in the systeminformation from the base station to the user equipments being servedthereby. Non-Patent Document 5 discloses the basic operation of a userequipment by PCI split. The user equipment that does not have the PCIsplit information needs to perform cell search using all PCIs (forexample, using all 504 codes). On the other hand, the user equipmentthat has the PCI split information is capable of performing cell searchusing the PCI split information.

Further, 3GPP has determined that the PCIs for hybrid cells are notcontained in the PCI range for CSG cells (see Chapter 10.7 of Non-PatentDocument 1).

In 3GPP, there are two modes in the method of selecting or reselecting aCSG cell by a user equipment. One is an automatic mode. The feature ofthe automatic mode is described below. The user equipment performsselection or reselection with the use of an allowed CSG list (allowedCSG ID list) in the user equipment. After the completion of PLMNselection, the user equipment camps on one cell in the selected PLMNonly in a case of a non-CSG cell or a CSG cell with a CSG ID present inthe allowed CSG list. The user equipment disables an autonomous searchfunction of the CSG cell if the allowed CSG list of the user equipmentis empty (see Chapter 5.2.4.8.1 of Non-Patent Document 3).

The second is a manual mode. The feature of the manual mode is describedbelow. The user equipment shows a list of available CSGs in thecurrently selected PLMN to the user. The list of CSGs provided to theuser by the user equipment is not limited to the CSGs included in theallowed CSG list stored in the user equipment. The user selects the CSGbased on the list of CSGs, and then the user equipment camps on the cellwith the selected CSG ID, to thereby attempt registration (see Chapter5.2.4.8.1 of Non-Patent Document 3).

The HeNB and HNB are required to support various types of service. Forexample, an operator causes the predetermined HeNB and HNB to registeruser equipments therein and allows only the registered user equipmentsto access the cells of the HeNB and HNB, so that the radio resourcesthat can be used by the user equipments are increased for performinghigh-speed communication. In such service, the operator correspondinglysets a higher accounting fee compared with normal service.

In order to achieve the above-mentioned service, the closed subscribergroup (CSG) cell that can be accessed only by the registered (subscribedor member) user equipments is introduced. It is required to deploy alarge number of closed subscriber group (CSG) cells in shopping malls,apartment buildings, schools, companies and the like. For example, theCSG cells are required to be deployed for each store in shopping malls,for each room in apartment buildings, for each classroom in schools, andfor each section in companies in such a manner that only the users whohave registered with the respective CSG cells are allowed to use thoseCSG cells. The HeNB/HNB is required not only to complement thecommunication outside the coverage of the macro cell but also to supportvarious types of service as described above. This leads to a case wherethe HeNB/HNB is deployed within the coverage of the macro cell.

In a case where a HeNB/HNB is deployed in the coverage of a macro cell,interference occurs between the HeNB/HNB and the macro cell. The radiowave from the macro cell interferes with the communication of the userequipment (UE), which is communicating with the HeNB/HNB in the coverageof the HeNB/HNB. Increased interference power due to the radio wave fromthe macro cell prevents a user equipment from communicating with theHeNB/HNB. On the other hand, in a case where a user equipmentcommunicating with a macro cell in the coverage of the macro cell movesinto the coverage of the HeNB/HNB deployed in the coverage of the macrocell, the interference of the radio wave from the HeNB/HNB interfereswith the communication with the macro cell. Increased interference powerdue to the radio wave from the HeNB/HNB prevents a user equipment fromcommunicating with a macro cell.

As a method of reducing the interference between a normal eNB (macrocell; macro eNB (MeNB)) and a HeNB, Non-Patent Document 8 discloses themethod of notifying a HeNB of the high interference indication (HII) andoverload indicator (OI) by a macro cell.

The HII is a signal for notifying, by a cell, an appropriate cell of thephysical resource that is apt to be interfered or desired not to beinterfered. As an example, in a case where there is a physical resourcedesired to be scheduled to a UE, the cell notifies a cell nearby of theHII for eliminating the interference to the physical resource. The cellnearby that has received the HII avoids the scheduling of the physicalresource to a UE being served thereby or lowers the power of thephysical resource, to thereby avoid interference.

The OI is a signal for notifying, by a cell, an appropriate cell of thephysical resource being influenced by the interference and itsinterference level or a fact that the level is higher than a threshold.As an example, in a case where there is a physical resource that isdesired to be scheduled to a UE or is scheduled, the cell notifies acell nearby of the OI for eliminating interference to the physicalresource. The cell nearby that has received the OI avoids the schedulingof the physical resource to a UE being served thereby or lowers thepower of the physical resource, to thereby avoid interference.

It is determined in the current 3GPP standards that the HII and OI maybe transmitted/received between macro cells by means of an X2 interface.However, in the current 3GPP standards, as shown in FIG. 7 , the X2interface is not provided between the eNB 72-1 being a macro cell andthe HeNB 72-2 and between the HeNBs 72-2.

Therefore, Non-Patent Document 8 describes that an X2 interface isprovided between a macro cell and a HeNB, between a macro cell and aHeNBGW and between a HeNBGW and a HeNB, and the macro cell notifies theHeNB of the HII and OI by means of the X2 interface. However, a HeNB isassumed to be used at home, and is also studied to be deployed so as tobe managed by a general user, not by an operator. The connection betweenHeNBs or between a macro cell and a HeNB by means of an X2 interface inthe case where a HeNB is deployed so as not to be managed by an operatorin this manner leads to a problem that the configuration becomescomplicated.

Non-Patent Document 9 discloses that a macro cell notifies a HeNB of theHII via a UE being served by the macro cell. It is proposed that thePRACH or UL-SCH be used as a channel on which notification is made froma UE to a HeNB. While Non-Patent Document 9 describes the channel onwhich notification is made from a UE to a HeNB but does not describeanything else, and the mechanism in which a macro cell notifies a HeNBof the HII is unclear. For example, a UE being served by a macro cellnormally does not know the RACH configuration of the HeNB. Accordingly,a UE being served by a macro cell cannot send the PRACH to a HeNB.Non-Patent Document 9 does not disclose the method of solving such aproblem.

In order to solve such a problem, the present invention discloses themethod of enabling a macro cell to notify a HeNB of the informationrelated to the interference (hereinafter, referred to as“interference-related information in some cases) to a physical resourceused at a macro cell, specifically, a signal for avoiding theinterference such as the HII and OI via a UE.

Non-Patent Document 9 discloses that a macro cell notifies a HeNB of theHII via the UE being served by the macro cell but does not specificallydisclose a HeNB is notified of the HII or a UE that notifies a HeNB ofthe HIT. In a case where it is considered that a large number of HeNBswill be deployed, the system will become complicated and a signalingload will become enormous unless HeNBs to be notified are limited. Inaddition, unless the UEs to be notified are limited, a signaling loadwill become enormous, and uplink interference will increase, leading tothe degradation of communication quality.

In order to solve such a problem, the present embodiment discloses themethod of limiting HeNBs to be notified of the HII and the method oflimiting the UEs to be notified of the HII. Disclosed here is the methodof limiting the HeNBs to be notified of the HII to the HeNBs within thecoverage of a macro cell.

FIG. 13 is a conceptual diagram in a case where HeNBs are deployed inthe coverage of a macro cell. In FIG. 13 , reference numerals 1301 to1313 denote UEs, reference numerals 1314 to 1321 and reference numerals1324 to 1326 denote HeNBs, and a reference numeral 1322 denotes an eNBbeing a macro cell. A reference numeral 1323 denotes the coverage of themacro cell 1322. The coverage 1323 corresponds to a large-scalecoverage. The HeNBs 1314 to 1321 are deployed within the coverage of themacro cell 1322, and the HeNBs 1324 to 1326 are deployed outside thecoverage of the macro cell 1322. The UEs 1301 to 1313 correspond to theUEs 71 of FIG. 7 described above, the HeNBs 1314 to 1321 and 1324 to1326 correspond to the Home-eNBs 72-2 of FIG. 7 that are small-scalebase station devices, and the macro cell 1322 corresponds to the eNB72-1 of FIG. 7 that is a large-scale base station device.

It is no use to notify HeNBs deployed outside the coverage 1323 of theHII by the macro cell 1322. This is because the UE being served by themacro cell 1322 is little influenced by the interference from the HeNBdeployed outside the coverage 1323 of the macro cell 1322 and, on theother hand, the UE being served by the HeNB deployed outside thecoverage 1323 of the macro cell 1322 is little influenced by theinterference from the macro cell 1322.

Accordingly, in the present embodiment, the HeNBs notified of the HIIare HeNBs deployed within the coverage 1323 of the macro cell 1322. Forexample, in the case of FIG. 13 , the HeNBs notified of the HII by themacro cell 1322 are the HeNBs 1314 to 1321 deployed in the coverage 1323of the macro cell 1322. The macro cell 1322 notifies the HeNBs 1314 to1321 of the HII via the UEs being served thereby. This limits the numberof HeNBs to be notified of the HII, which enables to reduce thesignaling load necessary for notification of the HII.

The macro cell is required to recognize HeNBs deployed in the coverageof the own cell. Disclosed here is the method of judging a HeNB deployedin the coverage of a macro cell. FIG. 14 is a diagram showing a sequenceexample of a mobile communication system in a case where a macro celljudges HeNBs deployed in the coverage. In Step ST1401, the HeNB measuresa surrounding radio wave environment, that is, performs measurements inpower-on or initialization, or while transmission is stopped. Inaddition, the HeNB measures the received power of cells present in itsvicinity and obtains the cell identities (PCIs) of the cells, to therebydetect the cells. In this case, a cell having the received power equalto or larger than a certain received power threshold may be detected.The received power threshold for cell detection may be preliminarilydetermined in a static manner.

In Step ST1402, the HeNB receives the broadcast information of the cellfrom the detected cell. This may be performed in the measurements. InStep ST1403, the HeNB that has received the broadcast information fromeach cell judges whether or not that cell is a macro cell. In order toenable this judgment, each cell may broadcast an indicator as to whetheror not the own cell is a macro cell or the information indicating a celltype. In this case, by obtaining the type of the detected cell from thereceived broadcast information in Step ST1403, the HeNB judges whetheror not that cell is a macro cell. Examples of the cell types include amacro cell, pico eNB (pico cell), node for hotzone cells, HeNB/HNB/CSGcell, relay node, and remote radio head (RRH).

In the case where it is possible to judge whether or not the cell is amacro cell from the identity (PCI) of the cell, the HeNB may omit toobtain the cell type in Step ST1403. In this case, the HeNB may judge asto whether the cell is a macro cell based on the PCI of the cellobtained in Step ST1401.

In Step ST1404, the HeNB associates the received power informationmeasured for each of the macro cells detected in the measurements withthe PCI of that macro cell, and notifies the MME/S-GW. On that occasion,the HeNB also notifies the cell identity (PCI) of the own HeNB. TheMME/S-GW corresponds to the MME/S-GW unit 73 shown in FIG. 7 describedabove.

The MME/S-GW may be notified in power-off operation. The informationindicating that power is turned off or the information indicating thatthe deletion from the HII notified HeNB list is requested may benotified in addition to the above-mentioned information. This enables totake, for example, the case where power is turned off when a HeNB ismoved by a user into account in the judgment as to whether a macro cellneeds to notify the HII.

In Step ST1405, the MME/S-GW notifies each macro cell of the PCI of theHeNB and the received power information of the macro cell measured bythe HeNB, based on the PCI of the macro cell received from each HeNB. AnS1 interface may be used in the notification to the macro cell. In acase where an X2 interface that directly connects the macro cell and theHeNB is provided, it suffices that the HeNB directly notifies the macrocell of the information on the received power measurement results andthe PCI of the own HeNB per macro cell.

Each macro cell that has received the measurement results by the HeNBand the PCI of the HeNB judges whether or not the HeNB is deployed inthe coverage of the own cell. The macro cell makes judgment using, forexample, the received power measurement results of the macro cell by theHeNB.

In this case, the macro cell sets the threshold indicating whether ornot a HeNB is in the coverage of the own cell (hereinafter, referred toas coverage judgment threshold) in advance and, in Step ST1406, comparesthe received power measurement value showing the received powermeasurement results per HeNB with the coverage judgment threshold. Themacro cell judges that the HeNB is in the coverage of the own cell ifthe received power measurement value is equal to or larger than thecoverage judgment threshold or judges that the HeNB is outside thecoverage of the own cell if the received power measurement value issmaller than the coverage judgment threshold. The macro cell moves toStep ST1407 in the case of judging that the HeNB is in the coverage ormoves to Step ST1408 in the case of judging that the HeNB is outside thecoverage.

In the case of judging that the HeNB is in the coverage in Step ST1406and moving to Step ST1407, in Step ST1407, the macro cell stores thatthe HeNB is in the coverage of the own cell. Accordingly, it sufficesthat a list (hereinafter, referred to as HII notified HeNB list) isprovided and the HeNB is added to the list. The HIT notified HeNB listincludes the cell identity (PCI) of the HeNB. Further, the HII notifiedHeNB list may include the received power value of the own cell that hasbeen measured by the HeNB together with the PCI of the HeNB. The HIInotified HeNB list may be stored in the EPC communication unit 901,protocol processing unit 903 or control unit 911 shown in FIG. 9 .

In the case of judging that the HeNB is outside the coverage in StepST1406 and moving to Step ST1408, in Step ST1408, the macro cell deletesthe HeNB from the HII notified HeNB list. In a case where the HeNB hasnot been found in the HII notified HeNB list, the macro cell performsnothing and moves to the next Step ST1409.

The processes described above allow the macro cell to judge the HeNBdeployed in the coverage of the own cell among the HeNBs notified of thereceived power measurement value of the own cell and store that HeNB inthe HII notified HeNB list.

In Step ST1409, the macro cell judges whether or not to notify the HeNBof the HII. The macro cell moves to Step ST1410 in a case of judging tonotify the HII, or in a case of judging not to notify the HII, does notnotify the HII and moves to the next process.

In Step ST1410, the macro cell judges whether or not a HeNB is the HeNBincluded in the HII notified HeNB list for judging as to which HeNB isthe HeNB to be notified of the HII. The macro cell moves to Step ST1411in a case of judging that a HeNB is the HeNB included in the HIInotified HeNB list, or in a case of judging that a HeNB is not the HeNBincluded in the HII notified HeNB list, in other words, a HeNB that isnot included in the HII notified HeNB list, performs nothing and movesto the next process. In Step ST1411, the macro cell notifies the HeNBincluded in the HII notified HeNB list of the HII.

The processes described above allow the macro cell to judge the HeNBdeployed in the coverage of the own cell among the HeNBs notified of thereceived power measurement value of the own cell and notify the HeNB ofthe HII as required.

In a case where a HeNB is moved by a user or the like, power may beturned on after being turned off once, or initialization may beperformed. The above-mentioned operation is performed upon this, wherebya macro cell is allowed to judge whether the HeNB is deployed in thecoverage of the own cell. This enables to add or delete the HeNB to orfrom the HII notified HeNB list. Therefore, it is possible to notify theHeNB of the HII as required.

While a macro cell is configured to judge which HeNB is deployed in thecoverage of the own cell and which HeNB is not deployed in the coverageof the own cell in the method described above, as another method, a HeNBmay be configured to judge whether or not it is deployed in the coverageof the macro cell. In this case, the measurement results of the HeNB maybe used.

FIG. 15 is a diagram showing a sequence example of a mobilecommunication system in a case where a HeNB judges whether or not it isdeployed in the coverage of a macro cell. The portions of FIG. 15corresponding to those of FIG. 14 are denoted by the same step numbers,and the processes thereof are not described in detail.

In Step ST1401, in the measurements in power-on or initialization, orwhile transmission is stopped, the HeNB measures the received power ofthe cells present in its vicinity and obtains the cell identities (PCIs)of the cells, to thereby detect the cells. In Step ST1402, the macrocell broadcast, to the HeNB, the coverage judgment threshold being thethreshold indicating whether or not the HeNB is within the coveragethereof as the broadcast information. In Step ST1402, the HeNB receivesthe broadcast information of the detected cell.

In Step ST1501, the HeNB that has received the broadcast informationfrom each cell obtains the coverage judgment threshold in addition tothe cell type information shown in FIG. 14 .

In Step ST1502, the HeNB compares the received power measured for eachmacro cell of the macro cells detected in the measurements and thecoverage judgment threshold broadcast from the macro cell. The HeNBjudges whether or not the received power of each macro cell is equal toor larger than the coverage judgment threshold of the macro cell. In thecase where the received power of the macro cell that has been measuredis equal to or larger than the coverage judgment threshold, the HeNBjudges that it is in the coverage of the macro cell and moves to StepST1503. Meanwhile, in the case where the received power of the macrocell that has been measured is smaller than the coverage judgmentthreshold, the HeNB judges that it is outside the coverage of the macrocell and moves to Step ST1504. The HeNB provides the information (whichmay be a parameter) indicating whether or not it is in the coverage ofthe macro cell.

In Step ST1503, the HeNB sets “being in the coverage” in the informationindicating whether or not the HeNB is in the coverage of the macro cell.Specifically, the cell identity of the macro cell may be associated withthe information, or the cell identity of the macro cell may be includedin the information.

In Step ST1504, the HeNB sets “being outside the coverage” in theinformation indicating whether or not the HeNB is in the coverage of themacro cell.

In Step ST1505, each HeNB notifies the MME/S-GW of the PCI and theinformation indicating “being in the coverage” or not per macro cell ofthe detected macro cells. On that occasion, the HeNB notifies the cellidentity (PCI) of the own HeNB as well.

In Step ST1506, the MME/S-GW notifies each macro cell of the PCI of theHeNB and the information indicating “being in the coverage” or not,based on the PCI of the macro cell that has been received from eachHeNB.

In Step ST1507, each macro cell that has received the informationindicating whether “being in the coverage” or not and the PCI of theHeNB judges whether or not the HeNB is deployed in the coverage of theown cell. In this judgment, the information indicating whether or notthe HeNB is in the coverage that has been notified from each HeNB. Themacro cell moves to Step ST1508 in the case of judging that the HeNB isdeployed in the coverage of the own cell, or moves to Step ST1509 in thecase of judging that the HeNB is not deployed in the coverage of the owncell, that is, in the case of judging that the HeNB is deployed outsidethe coverage.

In Step ST1508, the macro cell adds the HeNB whose informationindicating “being in the coverage” or not has been set as “being in thecoverage” to the HII notified HeNB list.

In Step ST1509, the macro cell deletes the HeNB whose informationindicating “being in the coverage” or not has been set as “being outsidethe coverage” from the HII notified HeNB list. After performing theprocesses of Step ST1508 and Step ST1509, the macro cell performs therespective processes of Step ST1409, Step ST1410 and Step ST1411.

Execution of the above-mentioned processes allows the macro cell tostore the HeNB deployed in the coverage of the own cell in the HIInotified HeNB list. In addition, the judgment as to whether or not theHeNB is in the coverage of the macro cell is substantially performed bythe HeNB and, also in that case, the macro cell is allowed to notify theHeNB deployed in the coverage of the own cell of the HII as required.

The macro cell may broadcast the coverage judgment threshold byincluding it in the MIB or SIB1. The transmission timing of the MIB orSIB1 has been determined, whereby it is possible to receive the MIB orSIB1 with fewer processes in a case where the HeNB performsmeasurements. The coverage judgment threshold may be determined inadvance as a static value or may be determined by being associated withthe transmission power of the macro cell. The correspondencetherebetween may be determined in advance as a table or may be derivedby a function.

Alternatively, the coverage judgment threshold disclosed in FIG. 14 andFIG. 15 may be identical to a received power threshold which is allowedto be used in the cell detection in Step ST1401. This enables to reduceparameters.

In the method described above, the HeNB judges whether or not it isdeployed in the coverage of a macro cell, and notifies the macro cell ofthe information indicating whether or not the HeNB is deployed in thecoverage, which is the judgment results. The information indicatingwhether “being in the coverage” or not requires only a smaller amount ofinformation compared with the received power measurement value of themacro cell, which enables to reduce the signaling amount from the HeNBto the macro cell. Further, the information indicating whether “being inthe coverage” or not may be one bit. This minimizes the amount ofinformation. It suffices that each macro cell is notified of thisinformation and the cell identity of the own HeNB.

While description has been given that the HeNB notifies the cellsdetected in the measurements of the information indicating whether ornot it is in the coverage of the macro cell, the HeNB may notify onlythe macro cell, in the coverage of which the HeNB has judged that it isdeployed, of the information indicating whether or not it is in thecoverage. In this case, the information indicating whether “being in thecoverage” or not may be the information indicating whether “beingdeployed in the coverage” or not. This enables to limit the macro cellsnotified of the information indicating whether “being in the coverage”or not, whereby it is possible to further reduce the signaling amountfrom the HeNB to the macro cell.

Different HeNBs use the same PCI in some cases. This is because thenumber of PCIS is limited. In this case, the macro cell cannot judge asto which of the HeNBs having the same PCI should be notified of the HII.In such a case, it suffices that the HeNB notifies each macro cell ofthe GCI as the cell identity of the own HeNB. It suffices that the GCIis used in place of the PCI of the HeNB in Step ST1404 and Step ST1405of FIG. 14 or Step ST1505 and Step ST1506 of FIG. 15 . It suffices thatthe macro cell manages the HII notified HeNB list according to the GCIof the HeNB. The GCIs are the identities specific to cells, which do notoverlap each other. This enables a macro cell to specify a HeNB.

Disclosed here is via which UE, the HeNB is notified of the HII. The UEspresent in the coverage of a macro cell are taken as UEs that arenotified of the HII for limiting the number of UEs to be notified of theHII.

In FIG. 13 , the macro cell 1322 notifies the HeNBs of the HII via theUEs 1301 to 1313 present in the coverage 1323 of the own macro cell. Themacro cell 1322 notifies the UEs 1301 to 1313 present in the coverage1323 of the information indicating that the HII is notified or the HII.This enables the macro cell 1322 to notify the HeNBs 1314 to 1321deployed in the coverage 1323 of the macro cell 1322 of the HII via theUEs 1301 to 1313. The UEs being served by the macro cell 1322, that is,the UEs which have the macro cell 1322 as a serving cell may be taken asthe UEs present in the coverage 1323 of the macro cell 1322. As aresult, the macro cell 1322 is not required to notify the UEs presentoutside the coverage 1323 of the information indicating that the HII isnotified or the HII.

The method disclosed in the present embodiment limits the number ofHeNBs to be notified of the HII, which enables to reduce the signalingload required for the notification of the HIT. In addition, the numberof the UEs to be notified of the HII can be limited, which enables toreduce the signaling load, reduce the uplink interference and improvethe communication quality.

Further, the macro cell 1322 is allowed to notify the HeNBs in thecoverage 1323 of the HII. Accordingly, the macro cell 1322 is allowed toschedule, to the UEs being served thereby, the physical resourcesnotified of the HeNBs in the coverage 1323 by the HII. This enables toavoid interference in the physical resources. The macro cell 1322 isallowed to flexibly schedule the physical resources to UEs being servedthereby, which enables to improve the scheduling efficiency and improvethe throughput as a cell.

The method above has disclosed that the HeNBs deployed in the coverageof the macro cell are notified of the HII. Meanwhile, it has beendisclosed that the HII is notified via the UE present in the coverage ofthe macro cell. However, as to the coverage of the macro cell describedabove, the coverage for a HeNB may be identical to or different from thecoverage for a UE. Typically, the range in which a UE can obtain thereceived power required for a UE to take a macro cell as a serving cell,that is, the received power required for satisfying the criteria in cellselection (Non-Patent Document 3), is referred to as the coverage of themacro cell. The received power may be identical to or different from thereceived power (coverage judgment threshold) for judging “being in thecoverage” by the HeNB.

In the case where the received power required for taking a macro cell asa serving cell is identical to the coverage judgment threshold, a UE isallowed to use the same criteria as the criteria of the received powerrequired for taking the macro cell as a serving cell by a UE.Accordingly, it is not required to separately provide the coveragejudgment threshold, which makes control easier.

Meanwhile, in the case where the received power required for taking amacro cell as a serving cell differs from the coverage judgmentthreshold, it is possible to flexibly set the relationship between theHeNB to be notified of the HII and the UE notified of the HII. Forexample, the coverage judgment threshold is set to be smaller than thereceived power required for taking a macro cell as a serving cell by aUE. This enables to notify the HeNBs deployed in a larger range than thecoverage for normal UEs of the HII. As a result of the HeNBs deployed ina range slightly larger than the coverage for UEs being notified of theHIT, it is possible to further reduce the interference to the UE thattakes the macro cell as a serving cell.

It has been described that interference is small between the UE beingserved by a macro cell and the HeNB deployed outside the coverage of themacro cell, where the interference with the HeNB in the range slightlylarger than the coverage of the macro cell, which is the maininterference, can be reduced. In particular, it is possible to furtherreduce the interference with a UE being served by a macro cell presentat the edge of the coverage of the macro cell. This further improves thescheduling efficiency of the UE present at the edge of the coverage,which enables to improve the communication rate. Therefore, it ispossible to further improve the throughput as a cell.

Meanwhile, in the case where the received power required for taking themacro cell as a serving cell by a UE differs from the received power forjudging that the HeNB is in the coverage (that is, coverage judgingthreshold), an offset parameter indicating a difference valuetherebetween may be provided. The offset parameter may be preliminarilydetermined in a static manner or may be broadcast from the macro cell asthe broadcast information. This enables to set the offset parameter insynchronization with the coverage for UEs. Alternatively, the offsetparameter may be determined per HeNB. In this case, the offset parametermay be notified from a HeNB to a macro cell, which may be notifiedtogether with the PCI of the own HeNB. This enables to set the offsetparameter per HeNB and enables a flexible operation such as setting inaccordance with the output power of a HeNB.

First Modification of First Embodiment

In the first embodiment, the UEs notified of the HII are the UEs beingserved by a macro cell for limiting the number of UEs to be notified ofthe HII. However, it is not determined as to which UE notifies the HIIto which HeNB. This leads to a case where one HeNB is notified of theHII from a plurality of UEs. FIG. 16 is a conceptual diagram in a casewhere only one HeNB is deployed in the coverage of a macro cell, and aplurality of UEs are present in the coverage of the macro cell. Theportions of FIG. 16 corresponding to those of FIG. 13 are denoted by thesame reference numerals, which are not described.

The plurality of UEs 1301 to 1313 are present and one HeNB 1314 isdeployed in the coverage 1323 of the macro cell 1322. In such a case,the plurality of UEs 1301 to 1313 being served by the macro cell 1322notify the one HeNB 1314 of the HII. This increases the signaling amountand interference in the macro cell 1322.

In order to solve the above-mentioned problem, the present modificationdiscloses the method of determining as to which UE notifies which HeNBof the HII. The present modification discloses the method of notifyingthe HII via the UE having the largest received power from the HeNB.

FIG. 17 is a diagram showing a sequence example of a mobilecommunication system in a case where the HII is notified via a UE havingthe largest received power from a HeNB. The portions of FIG. 17corresponding to those of FIG. 14 are denoted by the same step numbers,and the processes thereof are not described in detail. In FIG. 17 , amacro cell selects a UE having the largest received power from a HeNB.In addition, a serving cell is the macro cell.

In Step ST1701, the UE receives the broadcast information from a servingcell in advance. In Step ST1703, the UE measures a surrounding radiowave environment regularly or upon an instruction from a serving cell.In addition, the UE measures the received power of cells present in itsvicinity and obtains the cell identities (PCIs) of cells, to therebydetect cells. On this occasion, a cell having received power equal to orlarger than a certain received power threshold may be detected. Thereceived power threshold for cell detection may be preliminarilydetermined in a static manner or may be broadcast from a serving cell.The UE can receive the broadcast information and obtain the receptionpower threshold. In a case of performing measurements upon instructionfrom a serving cell, in Step ST1702, the serving cell may notify the UEof a measurement instruction message in advance. The measurementinstruction message may include a measurement configuration being thesetting contents of measurements.

In Step ST1704, the UE receives the broadcast information of thedetected cell. This may be performed in the measurements. In StepST1705, the UE that has received the broadcast information from eachcell judges whether or not the cell is a HeNB. It suffices that forenabling this judgment, each cell broadcasts the indicator as to whetheror not the own cell is a HeNB or the information indicating a cell type.Meanwhile, in a case where the PCI of the HeNB is preliminarilydetermined so as to differ from that of the serving cell, in StepST1703, the UE may obtain the PCI of a cell to judge whether or not thecell is a HeNB.

In Step ST1706, the UE notifies the serving cell of the received powerinformation measured for each HeNB in association with the cell identity(PCI) of the HeNB that has been detected in the measurements. On thatoccasion, the UE notifies the identity (UE-ID) of the own UE as well.The measurements results are reported regularly or upon instruction froma serving cell. Alternatively, the measurement results may be reportedin a case where, for example, a cell larger than a certain threshold isdetected, or the UE may notify the serving cell of the report at anappropriate timing.

In Step ST1707, the serving cell that has received the received powermeasurement results of a HeNB detected in the measurements by each UEand the PCI of the HeNB selects the UE having the largest received powerfrom the HeNB per HeNB.

In Step ST1708, the serving cell adds the information of the UE to theHII notified HeNB list. The HII notified HeNB list is a list that storesthe HeNBs to be notified of the HII, as disclosed in the firstembodiment, which may be created using the method disclosed in the firstembodiment. The list is not particularly required, and it suffices thatthe HeNB to be notified of the HII is associated with the selected UE.The UE information may be the UE-ID. In a case where the UE informationhas already been included in the HII notified HeNB list and the existingUE information differs from the newly selected UE information, the UEinformation may be corrected to the new UE information. Alternatively,in a case where the HeNB that has the existing UE information loses thenew UE information, the UE information may be deleted. Those may beperformed in a case where the notification of Step ST1706 is received ormay be regularly performed.

After the completion of the process of Step ST1708, the serving cellperforms each of the above-mentioned processes in Step ST1409 andST1410, and moves to Step ST1709. In Step ST1709, the serving cellnotifies the HeNB in the HII notified HeNB list of the HII via the UE inthe list.

Through execution of the processes above, the serving cell is allowed torecognize via which UE, it notifies the HeNB to be notified of the HIIof the HII. In the case of FIG. 17 , it is possible to notify the HeNBto be notified of the HII of the HII via the UE having the largestreceived power from the HeNB.

To describe the example of FIG. 16 , the macro cell 1322 is allowed tonotify the HeNB 1314 of the HII via the UE (in this case, UE 1303)having the largest received power from the HeNB 1314 among a pluralityof UEs present in the coverage 1323.

In a case where different HeNBs can use the same PCI, the GCI may beused as the cell identity of the HeNB. The HeNB broadcasts the GCI ofthe own HeNB. The UE receives the broadcast information of the HeNB andobtains the GCI of the HeNB in the measurements of a cell nearby. The UEmay notify the serving cell of the GCI as the cell identity of the HeNB.The serving cell may refer to the GCI of the HeNB in the HII notifiedHeNB list, to thereby add, correct or delete the UE-ID of the UE havingthe largest received power from the HeNB to, in or from the list. TheGCIs are the identities specific to cells, which do not overlap eachother. Therefore, the macro cell is allowed to specify the HeNB.

The method disclosed in the present modification enables the macro cellto notify each HeNB, which is to be notified of the HII, of the HII viaone UE. However, the UE is not necessarily selected for all HeNBsdeployed in the coverage of a macro cell. There is conceivable a casewhere there is a HeNB that is not included in the report on themeasurement results from UEs being served by the macro cell. In thiscase, however, the UEs being served by the macro cell include no UE thatreceives the transmission wave from the HeNB or receives the power equalto or larger than a specific received power threshold. This means thatthere is no UE influenced by the interference from the HeNB.Accordingly, it is not necessarily required to select a UE for the HeNBand notify the HeNB of the HII.

The HeNBs stored in the HII notified HeNB list in Step ST1708 of FIG. 17may be all HeNBs reported from the UE in Step ST1706. As a result, a UEis selected for the HeNB included in the HII notified HeNB list.

The method disclosed in the present modification enables to notify eachHeNB, which is to be notified of the HII, of the HII via one UE. Thisallows the macro cell to limit the UE to be notified of the informationindicating that the HIT is notified or the HII, to the UE. Further, theUE that notifies the HeNB of the HII can also be limited to the UE,which enables to further limit the number of UEs. Therefore, it ispossible to reduce the signaling load, reduce uplink interference, andimprove the communication quality.

The UE present at the edge of the coverage area of the macro celldetects, in measurements, the cell deployed outside the coverage for theHeNBs of the serving cell at times. In this case, the serving cell maylimit only the HeNB deployed in the coverage for the HeNB from the HeNBsnotified in the report on the measurement results from a UE by themethod of judging a HeNB deployed in the coverage for a HeNB, which isdisclosed in the first embodiment. This enables to further reduce thesignaling load, reduce uplink interference and improve communicationquality.

In the method disclosed above, there is a conceivable case where one UEnotifies a plurality of HeNBs of the HII. For example, the UE 1306 shownin FIG. 13 has the largest received power from the HeNB 1320 and theHeNB 1321 compared with other UEs. Therefore, the UE 1306 is selected asthe UE that notifies the HeNB 1320 and the HeNB 1321 of the HII. The UEthat has to notify a plurality of HeNBs of the HII consumes an increasedamount of power. In order to solve this problem, the HeNB notified ofthe HII by a UE may be limited to one. An example of that method isdisclosed below.

The macro cell selects a UE having the highest received power for allHeNBs notified in the report on the measurement results from UEs beingserved thereby. If a plurality of HeNBs select the same UE, the UE isselected for a HeNB having the highest received power by the UE. In thecase where a plurality of HeNBs select the same UE, a UE having thesecond-highest received power is selected for HeNBs that do not have thehighest received power. In the case where there is the UE that has notbeen selected among the UEs having the second-highest received power,that UE is selected. If the UE having the second-highest received powerhas been selected for another HeNB, a UE having the third-highestreceived power is selected. Similarly, if a UE having the n-th highestreceived power has been selected for another HeNB, a UE having the(n+1)th highest received power is selected.

The use of the procedure above causes one UE to limit a HeNB to benotified of the HII to one. For example, in the case described above,the UE 1306 is selected for the HeNB 1321, and the UE 1305 is selectedfor the HeNB 1320. The method disclosed here enables to prevent anincrease in power consumption of a specific UE.

Second Modification of First Embodiment

In the first modification of the first embodiment, a macro cell selectsa UE, through which the HII is notified, and notifies a HeNB of the HIIvia that UE. The present modification discloses the method of selecting,by a UE, a HeNB to be notified of the HII. As an example, a macro cellnotifies a UE being served thereby of the interference-relatedinformation, for example, the information indicating that the HII isnotified (hereinafter, referred to as “notification information” in somecases) or the HII, and the UE that has received the information judges aHeNB to be notified of the HII. Then, the UE notifies the HeNB judged tobe notified of the HII of the HII.

The macro cell broadcasts the notification information indicating thatthe HIT is notified or the HII being the interference-relatedinformation to UEs being served thereby. Alternatively, the macro cellnotifies UEs being served thereby of the notification informationindicating that the HII is notified or the HII by a dedicated signal.

The UE that has received the information determines whether or not tonotify the HeNB of the HII or determines a HeNB to be notified of theHIT, using the measurement results. As disclosed in the firstmodification of the first embodiment, in the measurements of cellsnearby, the UE measures the received power of a cell present in itsvicinity and obtains the cell identity (PCI) of the cell, to therebydetect a cell. In addition, the UE receives the broadcast information ofthe detected cell and judges whether or not the cell is a HeNB.

Accordingly, the UE recognizes the received power measurement value ofthe detected cell. Then, the UE compares the measurement result with thethreshold indicating whether or not to notify the HII, and stores thePCI of a HeNB whose received power measurement result is larger than thethreshold. The UE notifies the HeNB that has been stored among thedetected cells of the HII. The UE may store the PCI of the HeNB in theprotocol processing unit 801, application unit 802 or control unit 810shown in FIG. 8 , which may be stored as a list.

The threshold as to whether or not to notify the HII is broadcast by amacro cell to UEs being served thereby as the broadcast informationtogether with the notification information indicating that the HII isnotified or the HII being the interference-related information.Alternatively, the macro cell notifies a UE being served thereby as adedicated signal. Accordingly, the UE receives the broadcast informationor dedicated signal in advance, to thereby obtain the threshold.

In a case where the macro cell broadcasts the threshold, the thresholdmay be broadcast by being included in the SIM or SIB4. The transmissiontiming of the SIM has been determined, which enables the reception withfew processes at an early stage in the case where the HeNB performsmeasurements. The SIB4 includes the neighbor cell information, and ifthe threshold is included in the same block as the neighbor cellinformation, it is only required to obtain the SIB4 when a UE obtainsthe information related to the neighbor cell. This makes control simplerand reduces malfunctions in control.

Alternatively, the threshold may be preliminarily determined in a staticmanner. In this case, the macro cell is not required to broadcast thethreshold, which makes control simpler. Still alternatively, a pluralityof such thresholds may be provided, and the thresholds as to whether ornot to notify a plurality of HIIs may be listed in a table where thoseare respectively numbered, so that those numbers are broadcast. Thisenables the UE to determine whether or not to notify a HeNB of the HIIor determines a HeNB to be notified of the HII using the measurementresults of the cell nearby by the UE.

In the above-mentioned method, the UE stores the cell identity (PCI) ofa HeNB to be notified of the HII. The cell identity may be a GCI.Alternatively, in a case of, for example, performing measurements uponinstruction from a macro cell, a measurement ID may be stored in placeof the cell identity. The cell identity of the HeNB can be specified bythe measurement ID.

The method disclosed in the present modification limits the number ofUEs to be notified of the HII and eliminates the need for notifying, bya UE, a macro cell of the report on the received power measurementresults of the HeNB for HII notification. In addition, the macro cell isnot required to provide an instruction as to a HeNB to whichnotification is made. Therefore, the HeNB is not required to performmeasurements or notify the macro cell of the measurement results. Inaddition, the macro cell is not required to notify the UE of theinformation indicating a HeNB to be notified. Accordingly, the signalingload can be reduced.

Third Modification of First Embodiment

The present modification discloses another method for limiting HeNBs tobe notified of the HII. The HeNBs to be notified of the HII are HeNBspresent in a specific received power range from a macro cell. FIG. 18 isa conceptual diagram in a case where HeNBs are deployed in the coverageof the macro cell. The portions of FIG. 18 corresponding to those ofFIG. 13 are denoted by the same reference numerals, which are notdescribed. In FIG. 18 , portions of broken lines which are shown byreference numerals 1801-1 and 1801-2 denote ranges of specific receivedpower from the macro cell 1322. The reference numeral 1801-1 denotes afirst received power range, and the reference numeral 1801-2 denotes asecond received power range. For example, the HeNBs to be notified ofthe HII are the HeNBs deployed in the range between the first receivedpower range 1801-1 and the second received power range 1801-2. In FIG.18 , the HeNBs to be notified of the HII are the HeNB 1314, HeNB 1317and HeNB 1316. This enables to further reduce the number of HeNBs to benotified of the HII and reduce the signaling load required for thenotification of the HII.

The macro cell needs to recognize HeNBs deployed in the first receivedpower range 1801-1 and the second received power range 1801-2. Themethod of judging the HeNBs deployed in a specific received power rangecan be achieved by partly changing the method disclosed in the firstembodiment.

FIG. 19 is a diagram showing a sequence example of a part of the mobilecommunication system in a case of judging HeNBs deployed in a specificreceived power range. In the first embodiment, in Step ST1406 of FIG. 14, the macro cell compares the received power per macro cell that hasbeen reported from the HeNB with the coverage judgment threshold, tothereby judge whether or not the HeNB is deployed in the coverage. Inthe present modification, the macro cell performs the process of StepST1901 of FIG. 19 in place of the process of Step ST1406 of FIG. 14 .

In Step ST1901 of FIG. 19 , two range judgment thresholds, specifically,a first range judgment threshold and a second range judgment thresholdmay be provided, so that a macro cell compares the received power permacro cell reported from the HeNB with the two range judgment thresholdsto judge whether or not the HeNB is deployed in the coverage. The tworange judgment thresholds each correspond to a specific received powerrange.

In Step ST1901, the macro cell judges that the HeNB is in the twocorresponding received power ranges and moves to Step ST1407 in the casewhere the received power of the macro cell is equal to or smaller thanthe first range judgment threshold and the received power of the macrocell is equal to or larger than the second range judgment threshold, ormoves to Step ST1408 in the case where the received power of the macrocell is larger than the first range judgment threshold and the receivedpower of the macro cell is smaller than the second range judgmentthreshold.

In Step ST1407, the macro cell adds the HeNB to the HII notified HeNBlist. In Step ST1408, the macro cell deletes the HeNB from the HIInotified HeNB list. In a case where the HeNB has not been included inthe HII notified HeNB list, the macro cell performs nothing and moves tothe next step.

The processes above enable to further reduce the number of HeNBs to benotified of the HII and reduce the signaling load required for thenotification of the HII.

In a case where the physical resources are used depending on thereceived power from a macro cell, for example, in the case of afrequency resource reuse (FRR), it is possible to notify only a specificHeNB using the physical resource notified by the HII of the HII.

While FIG. 19 shows one specific received power range, the receivedpower range may not be limited to one and a plurality of received powerranges maybe provided. This enables to flexibly select HeNBs to benotified of the HII.

This method is also applicable to the method of judging whether or not aHeNB is in the coverage that is disclosed in the first embodiment. Inthe case where a HeNB makes judgment, it suffices that the macro cellbroadcasts the required number of range judgment thresholds.Accordingly, it is possible to obtain similar effects to those of thefirst embodiment.

This method is also applicable to the method of judging whether or notthe serving cell is in the coverage using the report on the measurementresults of UEs, similarly to the method disclosed in the firstmodification of the first embodiment. This enables the notification ofthe HII to the HeNB via the UE present in a specific received powerrange from a macro cell. Similarly, this method is also applicable tothe method disclosed in the second modification of the first embodiment.

Similarly to the coverage for UEs and the coverage for HeNBs disclosedin the first embodiment, the received power range for HeNBs to benotified of the HII may be identical to or different from the receivedpower range for UEs to be notified of the HIT. For example, in a casewhere the received power range for HeNBs to be notified of the HII islarger than the received power range for UEs to be notified of the HII,it is possible to further limit the number of UEs to be notified of theHII. Meanwhile, in a case where the received power range for UEs to benotified of the HII is larger than the received power range for HeNBs tobe notified of the HII, the number of UEs present in that rangeincreases, so that the HeNBs to be notified of the HII can be notifiedof the HII with reliability. Accordingly, it is possible to avoid theinterference according to the deployment of a macro cell and HeNBs.

Fourth Modification of First Embodiment

While the HeNBs to be notified of the HII are HeNBs present in a certainreceived power range from a macro cell in the first embodiment, in thepresent modification, the HeNBs to be notified of the HII are HeNBspresent in the range with a specific distance or a path loss from themacro cell.

The method of judging HeNBs deployed in the range of a specific pathloss from a macro cell is achieved by using the path loss in place ofthe received power disclosed in the first embodiment to the thirdmodification of the first embodiment. For example, in the case ofapplication to the first embodiment, in Step ST1401 of FIG. 14 , theHeNB is only required to derive a path loss. The path loss may bederived using the received power measurement results of a cell nearbyand the transmission power value of the cell that has been broadcastfrom the neighbor cell. In Step ST1404, Step ST1405 and Step ST1406 ofFIG. 14 , a path loss may be used in place of the received power permacro cell. Further, in Step ST1406, the threshold of a path loss may beused as the coverage judgment threshold so that the directions ofinequality signs are reversed. This is because the inverse of path losscorresponds to the distance from a macro cell, and thus the magnituderelation of the inverse of path loss is identical to the magnituderelation of the received power.

The configuration described above enables to reduce the number of HeNBsto be notified of the HII and reduce the signaling load required for thenotification of the HII. Further, it is possible to limit HeNBs to benotified of the HII in accordance with the situation of an uplink, andthus this is the method suitable for avoiding uplink interference. Thismethod is applicable to the methods disclosed in the first embodiment tothe third modification of the first embodiment. In any of the cases, itsuffices that the method is performed as described above using a pathloss in place of the received power, and it is possible to obtainsimilar effects to those of the first embodiment to the thirdmodification of the first embodiment.

While the method involving the use of a path loss has been described,not a path loss but a distance may be used. In a case of application tothe method of judging whether or not a HeNB is in a coverage by a macrocell, which has been disclosed in the first embodiment, it suffices thatthe HeNB measures the location of the own HeNB using the GPS or the likein Step ST1401 shown in FIG. 14 and notifies the macro cell of thelocation information in Step ST1404 and Step ST1405. The macro cell maymeasure the location of the own cell using the GPS or the like andderive, using the location information of the own cell and the locationinformation notified from a HeNB, the distance between the own cell andthe HeNB. The macro cell may judge whether or not a HeNB is in acoverage based on the distance derived in Step ST1406. The coveragejudgment threshold may be expressed in distance as well.

Similarly, the application to the method of judging whether or not aHeNB is in the coverage by the HeNB is enabled as well. In this case, itsuffices that the macro cell broadcasts the location information of theown cell in Step ST1402 of FIG. 15 . Similarly, in the case of themethod involving the use of the measurements of a UE disclosed in thefirst modification of the first embodiment, the UE may measure thelocation of the own UE using the GPS or the like and notify a macro cellof the location information. A HeNB may be notified of the HII via a UEpresent in a specific distance range. The same holds true for the secondmodification of the first embodiment, and the above-mentioned methodsenable to obtain similar effects to those of the second modification ofthe first embodiment.

Similarly to the coverage for UEs and the coverage for HeNBs disclosedin the first embodiment, the path loss range or distance range for HeNBsto be notified of the HII may be identical to or different from the pathloss range or distance range for UEs to be notified of the HII. Also inthis case, effects similar to those of the first embodiment can beobtained.

Fifth Modification of First Embodiment

While the HeNBs notified of the HII are HeNBs present in a specificreceived power range from a macro cell in the first embodiment, in thepresent modification, HeNBs notified of the HII are HeNBs present in aspecific direction range with respect to a macro cell.

The method of judging HeNBs deployed in a specific direction range withrespect to a macro cell is achieved with the use of the locationinformation disclosed in the fourth modification of the firstembodiment. From the location information of the HeNB and the locationinformation of the macro cell, it is possible to derive a direction inwhich the HeNB is deployed with respect to the macro cell. Therefore, itsuffices that whether or not a HeNB is in a specific direction range isjudged based on the information on the direction with respect to themacro cell, which has been derived from the location information.

Further, from the location information of a UE and the locationinformation of a macro cell, it is possible to derive a direction inwhich the UE is deployed with respect to the macro cell. Therefore, itsuffices that a HeNB is notified of the HII via a UE present in aspecific direction range based on the information on the direction withrespect to the macro cell that has been derived from the locationinformation.

As another method of judging a specific direction range with respect toa macro cell, angle of arrival (AoA) information may be used. The AoA isobtained by deriving the arriving direction of a received wave receivedby a macro cell from an angle relative to a specific direction. Themacro cell is capable of recognizing the direction in which each UE ispresent through reception of a transmitted wave from the UE being servedthereby. Therefore, it suffices that a macro cell recognizes a UEpresent in a specific direction range and notifies a HeNB of the HII viathe UE based on the AoA information method of the UE. This enables tospecify HeNBs to be notified of the HIT as the HeNBs in a specificdirection range. The interference of physical resources notified by theHII can be reduced for the HeNBs present in a specific direction range,whereby it is possible to schedule the physical resources notified bythe HII to the UEs present in its direction range. This is effective ina case where physical resources are used according to a direction.

Further, similarly to the coverage for UEs and the coverage for HeNBsdisclosed in the first embodiment, the direction range for HeNBs to benotified of the HII may be identical to or different from the directionrange for UEs to be notified of the HII. Also in this case, similareffects to those of the first embodiment can be obtained.

Sixth Modification of First Embodiment

The first modification of the first embodiment has disclosed the methodof selecting, by a macro cell, a UE having the highest received powerfor all HeNBs notified in the report on the measurement results from UEsbeing served thereby, to thereby notify the HII via the UE. The presentmodification discloses the method of notifying the HII via a UE presentin a specific received power range from a HeNB.

FIG. 20 is a conceptual diagram in a case where HeNBs are deployed inthe coverage of a macro cell. The portions of FIG. 20 corresponding tothose of FIG. 13 are denoted by the same reference numerals, which arenot described. In FIG. 20 , the portions of broken lines which areindicated by reference numerals 2001-1 to 2001-8 denote ranges ofspecific received power from the HeNBs 1314 to 1321, respectively.

For example, the HeNBs notified of the HII are HeNBs in the coverage ofthe macro cell, and the HeNBs are notified of the HII via UEs present inspecific received power ranges from the respective HeNBs. In FIG. 20 ,the HeNB 1314, HeNB 1315, HeNB 1316, HeNB 1318, and HeNB 1321 arenotified of the HII via the UE 1311, UE 1301 and UE 1310, UE 1312, UE1313, and UE 1306, respectively. In a case where there is no UE presentin a specific received power range from a HeNB, the HII is not notified.The HeNB 1317, HeNB 1319 and HeNB 1320 are not notified of the HII.

The macro cell needs to recognize a UE present in a specific receivedpower range from the HeNB. This method is achieved by partly changingthe method disclosed in the first modification of the first embodiment.

FIG. 21 is a diagram showing a sequence example of a part of a mobilecommunication system in a case where the HII is notified via a UEpresent in a specific received power range from a HeNB. In the firstmodification of the first embodiment, in Step ST1707 of FIG. 17 , amacro cell selects a UE having the largest received power from the HeNBper HeNB based on the received power per HeNB reported from a UE. Then,in Step ST1 708, the HeNB and the selected UE are associated with eachother and stored in the HII notified HeNB list. In the presentmodification, the process of Step ST2101 of FIG. 21 is performed inplace of Step ST1707 of FIG. 17 .

The HeNB range threshold for judging whether or not a UE is in aspecific received power range from a HeNB has been provided and, in StepST2101 of FIG. 21 , the macro cell selects a UE having the receivedpower from the HeNB that is equal to or larger than the threshold perHeNB.

Next, in Step ST1708, the macro cell associates the HeNB with theselected UE and stores those in the HIT notified HeNB list. A pluralityof UEs may be selected. In this case, a plurality of UEs may beassociated with the HeNB and stored in the list as well. The processesabove enable to notify the HeNB of the HII via a UE present in aspecific range of the received power from a HeNB. This enables toexclude UEs present outside the specific range, whereby it is possibleto reduce a signaling load, reduce uplink interference, and improvecommunication quality.

The HeNB range threshold is set by a macro cell, which may beindividually set by each HeNB. In this case, it suffices that each HeNBnotifies a macro cell nearby of the HeNB range threshold by means of theS1 interface. It suffices that in Step ST2101, the macro cell makesjudgment with the use of an individual HeNB range threshold notifiedfrom the HeNB. This enables to select a UE present in specific receivedpower in accordance with a situation per HeNB, for example, the outputpower of the HeNB. The application to a case where various HeNBs will bedeployed enables to flexibly deploy the HeNBs.

In the description above, the macro cell selects a UE present in aspecific received power range from a HeNB. As another method, a UE mayjudge whether or not it is in a specific received power range from aHeNB. This method is achieved by partly changing the method disclosed inthe first modification of the first embodiment. For allowing judgment bya UE, the method of judging whether or not a HeNB is in the coverage ofa macro cell by a HeNB, which has been disclosed in the firstembodiment, may be applied to the UE.

For example, a UE performs the processes of Step ST1502 to Step ST1504of FIG. 15 after the process of Step ST1705 of FIG. 17 . On thisoccasion, in Step ST1502, judgment is made using the received power of aHeNB in place of the received power of a macro cell and using theabove-mentioned HeNB range threshold in place of the coverage judgmentthreshold. Based on the results thereof, in Step ST1706 of FIG. 17 , theUE may notify the serving cell being a macro cell of each of the HeNBspresent in the HeNB range threshold and the UE-ID of the own UE. Afterreceiving the notified information, the serving cell being a macro celldoes not perform the process of Step ST1707 and moves to Step ST1708and, in Step ST1706, adds, corrects or deletes the UE information of theHII notified HeNB list based on each of pieces of the notified HeNBinformation and the UE information corresponding thereto.

The HeNB range threshold may be preliminarily determined in a staticmanner, or may be set by each HeNB and broadcast by each HeNB. The UE isallowed to obtain the HeNB range threshold by receiving the broadcastinformation of the HeNB detected in the measurements of neighbor cells.Then, with the use of this, the UE is allowed to judge whether or not itis in a specific range from the HeNB.

The method of selecting a UE having the largest received power from aHeNB disclosed in the first modification of the first embodiment may becombined with the method disclosed in the present modification. It ispossible to further limit the UEs to be notified of the HII by selectinga UE being in a specific received power range and having the largestreceived power from a HeNB. This enables to further reduce a signalingload, reduce uplink interference, and improve communication quality.

Seventh Modification of First Embodiment

The present modification discloses another method of making, via whichUE, notification by a macro cell. The macro cell notifies the HeNB ofthe HII via a UE in a connected state, specifically, in theRRC_Connected state.

The macro cell notifies the UE in the RRC_Connected state among UEsbeing served thereby of the indication that the HII is notified or theHII, and the UE in the RRC_Connected state that has received thatinformation notifies a HeNB of the HII. This limits the number of UEs tobe notified of the indication that the HII is notified or the HII fromthe macro cell. In addition, it is possible to limit the number of UEsthat notify the HeNBs of the HII.

As the method of notifying the UE in the RRC_Connected state of theindication that the HII is notified or the HII from the macro cell, RRCsignaling or MAC signaling may be used. The RRC connection has beenestablished in the UE in the RRC connected state, and accordingly it isnot required to newly establish RRC connection for notifying theinformation. Accordingly, a complicated process is not required, wherebynotification can be made with a small control delay.

In the case of using MAC signaling, notification may be made by newlyproviding a MAC control element for the notification, notification maybe made using a MAC service data unit (SDU), or notification may be madeusing a padding bit that is an option in the current standard.

In the case of using MAC signaling, control can be made much easier. Ascheduler of a macro cell manages the contents of the HII, such as aphysical resource in which interference is avoided. The scheduler isprovided in the protocol control unit 903 or control unit 911 of FIG. 9. In addition, the scheduler processes MAC signaling. Accordingly, thescheduler of the macro cell processes the indication that the HII isnotified, and the notification contents setting of the HII and thenotification thereof. Accordingly, it is possible to make control in amacro cell easier.

Eighth Modification of First Embodiment

The present modification discloses another method of making, via whichUE, notification by a macro cell. The macro cell notifies the HeNB ofthe HII via the UE in an idle state, specifically, in the RRC_Idlestate.

The macro cell notifies the UE in the RRC_Idle state among UEs beingserved thereby, and the UE in the RRC_Idle state that has received theinformation notifies the HeNB of the HII. This limits the number of UEsnotified of the indication that the HII is notified or the HII from themacro cell. In addition, it is possible to limit the number of UEs thatnotify the HeNB of the HII. As the method of notifying the UE in theRRC_Idle state of the indication that the HII is notified or the HITfrom the macro cell, it suffices that the macro cell broadcasts it tothe UE being served thereby. The UE in the RRC_Idle state being servedby the macro cell is capable of receiving the broadcast information fromthe macro cell. In the case of broadcasting by a macro cell, the SIB1,SIB4 or new system information block (SIB) may be provided.

The broadcast timing of the SIB1 has been determined in advance, wherebythe UE is allowed to receive the broadcast information at an earlystage. The SIB4 includes the information of a neighbor cell. Forexample, in the case where, a macro cell determines a HeNB to benotified of the HIT, the receiving operation of a UE can be simplifiedby including the indication that the HII is notified or the HII contentsand the information of a HeNB notifying the above in the SIB andnotifying those. As a result of providing a new SIB, similarly, theindication that the HII is notified or the HII contents and theinformation of a HeNB that notifies the above are included in the newSIB and notified. A UE is allowed to make judgment only from this SIB,whereby it is possible to simplify the receiving operation of the UE andreduce control malfunctions.

Further, in notifying the HeNB of the HII, notification is enabled usingthe PRACH without changing the state of a UE, via a UE in the RRC_Idlestate. Accordingly, the UE does not need to perform a complicatedprocess and is allowed to make notification with a small control delay.

The broadcast information is corrected per certain period. In the caseof being notified of the information that the broadcast information hasbeen corrected, the UE has to wait for the next period to receive thebroadcast information. The macro cell may make notification using, notbroadcast information but paging for reducing the latency. It sufficesthat notification is made by including the indication that the HII isnotified or the HII in the PCH or PCCH.

In the case of notifying a UE being served thereby with the use ofpaging, the macro cell is capable of notification limited to a UE to benotified of the HII. Normally, paging is sent from the MME. In a casewhere the MME can judge a macro cell in which notification is necessary,a HeNB to be notified of the HII, or a UE via which notification ismade, it suffices that paging is transmitted from the MME to the macrocell and the macro cell notifies the UE. In a case where the MME cannotjudge a macro cell in which notification is necessary, a HeNB to benotified the HII, or a UE via which notification is made, it sufficesthat a macro cell managed by the MME is notified of the paging, andjudgment is made as to whether or not the own cell should makenotification per macro cell that has received the paging.

Alternatively, the macro cell may send the paging for HII. The macrocell recognizes the transmission timing of paging. Further, notificationis only required within the coverage of the macro cell and, unlike anormal case, the MME does not need to send paging. The macro cell isallowed to send the paging for HII. This enables to reduce the signalingamount from the MME to the macro cell.

In order to reduce the latency for correcting the broadcast information,the macro cell may notify the UE of the information indicating that theHII is notified or the information indicating that the HII istransmitted in the broadcast information, using paging. The UE that hasreceived the information may receive the information without waiting forthe latency for correcting the broadcast information.

This method can be implemented in a similar manner to that of theearthquake and tsunami warning system (ETWS) standardized by 3GPP. Themethod of broadcasting from a macro cell, method involving the use ofpaging, and method involving the use of the method similar to the ETWSdescribed above are applicable not only to a UE in the RRC_Idle statebut also to a UE in the RRC_Connected state. As another method ofnotifying a UE in the RRC_Idle state of the indication that the HII isnotified or the HII from a macro cell, the macro cell may establish theRRC connection with the UE using paging, and after the establishment ofthe RRC connection, may make notification using the RRC message or MACmessage. The RRC connection is established once, and thus it is possibleto make the process after the RRC connection identical to the method ofnotifying a UE in the RRC_Connected state. Alternatively, notificationis not made after the RRC connection is established, but notificationmay be made using the RRC connection request message to be transmittedto a macro cell after the UE receives paging. The RRC connection requestmessage includes the indication that the HII is notified or the HIIinformation. This enables to make notification earlier compared with thenotification after the RRC connection is established, which enables toreduce a control delay.

The methods disclosed in the first embodiment to the eighth modificationof the first embodiment may be appropriately used in combination. Thisenables to limit HeNBs to be notified of the HII and also limit UEs thatnotify HeNBs of the HII, according to the circumstances. In a case wherea large number of HeNBs will be deployed or in a case where a generaluser will deploy HeNBs, the interference between a macro cell and a HeNBcan be reduced. Accordingly, it is possible to provide high-speed andhigh-capacity communication.

Second Embodiment

As described above, Non-Patent Document 9 proposes the use of the PRACHand UL-SCH as the channels for notification from a UE to a HeNB but doesnot describe anything else, and the mechanism in which a macro cellnotifies a HeNB of the HII is unclear. For example, a UE being served bya macro cell normally does not know the RACH configuration of a HeNB.Therefore, a UE being served by a macro cell cannot transmit the PRACHto a HeNB.

In order to solve the above-mentioned problem, the present embodimentdiscloses a specific mechanism in which a macro cell notifies a HeNB ofthe HII via a UE. As a specific mechanism in which a macro cell notifiesa HeNB of the HII via a UE, the present embodiment discloses the methodof notifying, by a UE, a HeNB of the HII using the RACH configuration ofthe HeNB.

FIG. 22 is a conceptual diagram in a case where a UE notifies a HeNB ofthe HII using the RACH configuration of the HeNB. In FIG. 22 , referencenumerals 2201, 2207 and 2213 denote UEs, a reference numeral 2204denotes an eNB (macro cell), and a reference numeral 2209 denotes aHeNB. The UEs 2201, 2207 and 2213 correspond to the UEs 71 of FIG. 7described above, the HeNB 2209 corresponds to the Home-eNB 72-2 of FIG.7 that is a small-scale base station device, and the macro cell 2204corresponds to the eNB 72-1 of FIG. 7 that is a large-scale base stationdevice.

The UEs 2201 and 2207 are UEs being served by the macro cell 2204. TheUE 2213 is a UE being served by the HeNB 2209. In FIG. 22 , referencenumerals 2203 and 2205 denote downlinks from the macro cell 2204 to theUEs 2201 and 2207, respectively, reference numerals 2202 and 2206 denoteuplinks from the UEs 2201 and 2207 to the macro cell 2204, respectively,a reference numeral 2211 denotes a downlink from the HeNB 2209 to the UE2213, and a reference numeral 2212 denotes an uplink from the UE 2213 tothe HeNB 2209. In FIG. 22 , a reference numeral 2210 denotes theinterface between the macro cell 2204 and the HeNB 2209, and a referencenumeral 2208 denotes the PRACH transmitted from the UE 2207 to the HeNB2209.

In a case of notifying the HeNB 2209 of the HII, the macro cell 2204notifies the HeNB 2209 of the HII via the UE 2207 being served by theown macro cell 2204. For example, by the methods disclosed in the firstembodiment to the eighth modification of the first embodiment, the UE2207 that has been notified of the indication that the HeNB 2209 isnotified of the indication that the HII is notified or the HII from themacro cell 2204 transmits the HII to the HeNB 2209. As a result of theRACH configuration of the HeNB 2209, the UE 2207 performs uplinktransmission to the HeNB 2209 using the PRACH 2208 and notifies the HII.This allows the macro cell 2204 to notify the HeNB 2209 of the HII viathe UE 2207 being served thereby.

However, a UE being served by a macro cell normally does not recognizethe RACH configuration of a HeNB, which leads to a problem that the UEbeing served by the macro cell cannot transmit the PRACH to the HeNB.Therefore, it is necessary for a UE to recognize the RACH configurationof a HeNB for implementing the method disclosed above. A specificexample of the method of acquiring the RACH configuration parameter of aHeNB by a UE is disclosed below.

TS36.213 V9.0.1 (hereinafter, referred to as “Non-Patent Document 11”)by 3GPP discloses that the RACH configuration is notified between eNBsby means of the X2 interface for a self organized network (SON).Meanwhile, the X2 interface is not supported in the HeNB. Accordingly,the RACH configuration cannot be notified by the HeNB using the methoddisclosed in Non-Patent Document 11. Therefore, a HeNB notifies a nodenearby of the RACH configuration parameter of the own cell by means ofthe S1 interface. As a specific example, the S1 interface is used as theinterface 2210 between the macro cell 2204 and the HeNB 2209 of FIG. 22.

Disclosed below is a specific example as to how to determine a nodenearby to be notified of the RACH configuration parameter of the owncell by the HeNB. A node nearby to be notified of the RACH configurationparameter of the own cell by a HeNB is determined based on themeasurement results of a surrounding radio environment of the HeNB.Specific examples of the surrounding radio environment includemeasurement results of a cell nearby. Specific examples of themeasurement results of a cell nearby include the reception quality,received power and path loss.

A HeNB selects, as a node to be notified of the RACH configurationparameter of the own cell, a node whose reception quality or receivedpower is equal to or larger than a threshold (or larger than athreshold) in the measurement results of a surrounding radioenvironment. Alternatively, if the path loss of a node is smaller than(or equal to or smaller than) a threshold in the measurement results ofa surrounding radio environment, a HeNB selects that node as a node tobe notified of the RACH configuration parameter of the own cell. TheHeNB may notify one or a plurality of nodes of the RACH configurationparameter of the own cell. The HeNB selects a node to be notified of theRACH configuration parameter of the own cell by the method describedabove, whereby it is possible to select a node nearby. This eliminatesthe need to notify even an unnecessary node of the RACH configurationparameter of the own cell, and accordingly, the processing load of theHeNB can be alleviated.

For example, in the method disclosed in the first embodiment, a HeNBnotifies the selected node of the PCI and received power information pernode and the PCI of the own HeNB and, on this occasion, may notify theRACH configuration parameter of the own HeNB. In the example disclosedin FIG. 14 , a HeNB obtains the information of a cell type and selectsonly a macro cell in Step ST1403. Accordingly, in Step ST1404, a HeNBnotifies the PCI and received power information per macro cell and thePCI of the own HeNB in Step ST1404 and, on this occasion, may notify theRACH configuration parameter of the own HeNB.

In a case where it is required to notify the HeNB of the HII via a UE,the macro cell that has been notified of the RACH configurationparameter of the HeNB notifies a user equipment (UE) being servedthereby of the information. Two specific examples of the notificationmethod are disclosed below: (1) notification is made using the broadcastinformation; and (2) notification is made using a dedicated signal.

Disclosed here is a specific example in which a macro cell notifies aHeNB of the HII using the broadcast information in the LTE and LTE-A.The RACH configuration is used as the broadcast information. Twospecific examples in the case of using the RACH are disclosed below: (1)a RACH configuration for a serving cell, that is, for a node that hasbeen notified of the configuration parameter of uplink transmission of aHeNB and a RACH configuration for a HeNB are provided in the currentRACH configuration; and (2) a RACH configuration is provided apart fromthe current RACH configuration.

In a case where the macro cell notifies UEs being served thereby of theHII dedicatedly using a dedicated signal, the RACH configuration may benotified together with the information indicating that the HIT isnotified or the HII. In addition, for recognizing a HeNB, to which theRACH configuration is provided, the cell identity of a correspondingHeNB is notified together with the RACH configuration. The cell identitymay be the PCI or GCI. In the case of the GCI, it is possible toeliminate a problem that a HeNB is confused with another HeNB due tooverlapping of PCIS.

In a case of notifying a UE being served thereby of the HII using thebroadcast information, or in a case of dedicatedly notifying a UE of theHII using a dedicated signal, the macro cell 2204 that has received thenotification of the RACH configuration parameter of the HeNB from theHeNB 2209 of FIG. 22 notifies the UEs 2201 and 2207 being served therebyof the HII via the downlinks 2203 and 2205, respectively. For example,in the case of dedicatedly notifying a specific UE of the HII, the macrocell 2204 notifies the UE 2207 being served thereby of the HII via thedownlink 2205.

Two specific examples of the RACH configuration parameters are disclosedbelow.

(1) RACH configuration. Further, specific examples in the LTE and LTE-Ainclude “RACH-ConfigCommon” and “PRACH-config” (see TS36.331 V9.0.0(hereinafter, referred to as “Non-Patent Document 10”) by 3GPP).

(2) Uplink frequency information. The uplink frequency information usedbetween a HeNB and a user equipment being served thereby. Specificexamples of the uplink frequency information include a carrierfrequency, frequency band and component carrier. Specific examples inthe LTE and LTE-A include “freqInfo”, “ul-CarrierFreq” and“ul-Bandwidth” (see Non-Patent Document 10).

A component carrier is described below. As to the LTE-A system, it isconsidered to support transmission bandwidths larger than thetransmission bandwidths of the LTE system (see Non-Patent Document 6 andNon-Patent Document 7). For this reason, it is considered that a userequipment supporting the LTE-A simultaneously receives one or aplurality of component carriers (CCs). It is considered that a userequipment supporting the LTE-A has the capability for carrieraggregation of the reception and transmission, only reception, or onlytransmission simultaneously on a plurality of component carriers.

The present embodiment has described the RACH configuration parameters,not limited to the RACH configuration parameters, which may beparameters used for a UE to perform uplink transmission to a HeNB thatnotifies the HII. This enables a macro cell to notify a UE of theparameters for performing uplink transmission to a HeNB. The UE canperform the same procedure as that in establishment of a normal uplinkfor the HeNB, and thus exceptional control is not required when anuplink is established for a HeNB, which makes the control of a UEsimpler.

Further, a macro cell notifies a UE of the parameter for performinguplink transmission to a HeNB in advance before notifying the HeNB ofthe HII, whereby it is possible for a UE to immediately notify, in acase of receiving the indication that the HII is notified or the HIIfrom a macro cell, a HeNB of the HII using the parameter for performinguplink transmission. Accordingly, it is possible to reduce a controldelay when a macro cell notifies a HeNB of the HIT. This enables thescheduling for avoiding interference in accordance with the dynamicallychanging situation of interface.

The UE that has received the indication that the HII is notified or theHII from a macro cell notifies a given HeNB of the HIT. The methoddisclosed in the first embodiment may be used for determining a HeNB tobe notified. Six specific examples of the notification method aredisclosed below: (1) notification is made using the PRACH; (2)notification is made using the UL-SCH; (3) notification is made by beingmapped on the RRC establishment request (or included therein, ortogether therewith); (4) notification is made by being mapped on the RRCmessage; (5) notification is made by being mapped on the NAS message;and (6) notification is made by MAC signaling.

Disclosed below is a specific example in the case where a given HeNB isnotified of the HII using the PRACH. Non-Patent Document 9 describes thenotification using the PRACH but does not describe how to use the PRACH.The PRACH is a signal transmitted by a UE in the start of uplinktransmission. Therefore, in the case of receiving the PRACH, a HeNBcannot recognize whether the PRACH is the HII or the normal PRACH in thestart of uplink transmission by the technique of Non-Patent Document 9.Although the information for specifying a desired physical resource isrequired as the HII, in the technique of Non-Patent Document 9, it isunclear how to map the information on a conventional PRACH. In order tosolve the above-mentioned problem, the present embodiment disclosesbelow how to notify the HII using the PRACH.

(1) At least any one of the preamble sequence of the PRACH and physicalresources on a frequency-time axis used in the PRACH are caused tocorrespond to a desired physical resource.

(2) At least any one of the preamble sequence of the PRACH and physicalresources on a frequency-time axis used in the PRACH are partitioned forHII notification and for normal PRACH in advance.

(3) At least one of a bit indicating a physical resource and a bitindicating a use is associated with the PRACH.

In a case where the preamble sequence of the PRACH is caused tocorrespond to a desired physical resource, it suffices that one preamblesequence is caused to correspond to one or a plurality of physicalresource blocks (PRBs). This correspondence may be preliminarilydetermined in a static manner.

The UE that has received the indication that the HII is notified or theHII from a macro cell may select the contents of the HII, that is, thepreamble sequence of the PRACH corresponding to a desired physicalresource expected to avoid interference, and then notify a HeNB of theHII using the PRACH. The HeNB that has received the PRACH is capable ofspecifying a physical resource by the preamble sequence of the PRACH andpreventing scheduling of the physical resource to a UE being served bythe own HeNB.

As another method, a macro cell notifies a UE to be notified of the HIIof the corresponding preamble sequence. The macro cell may notify theHII using the broadcast information or may dedicatedly notify the HIIusing a dedicated signal. The macro cell may notify a UE together withthe indication that the HII is notified or the HII. The UE transmits thePRACH using the notified preamble sequence, which results intransmitting the HII. In this case, the correspondence informationbetween the physical resource and the preamble sequence may be sharedbetween the HeNB and the macro cell. The correspondence information maybe notified in advance from the HeNB to the macro cell or from the macrocell to the HeNB. Alternatively, the correspondence information may benotified from the HeNB to the macro cell together with the RACHconfiguration. This enables the HeNB that has received the PRACH of thepreamble sequence to specify a physical resource and prevent schedulingof the physical resource to a UE being served by the own HeNB.

The same holds true for the case in which the physical resource on afrequency-time axis used in the PRACH is caused to correspond to adesired physical resource. In this case, there may be used a PRACHconfiguration index for instructing a physical resource on afrequency-time axis to be used in the PRACH.

The correspondence may be preliminarily determined in a static manneralso in a case where the physical resource may differ between one forHII and the other for PRACH. Further, the correspondence may bebroadcast by a cell in advance. The SIB1 or SIB2 may be used. The use ofthe above-mentioned method enables to notify the HII without increasingthe bit number of the PRACH. In a case where the PRACH is associatedwith a bit indicating the use, the bit number may be one bit for showingone for the HII and the other for a normal PRACH. This enables todistinguish one for the HII from the other for a normal PRACH. Theabove-mentioned methods may be used in combination.

In the case of notifying the HII using the PRACH, the UE is onlyrequired to perform uplink transmission to a HeNB and does not need toreceive a downlink signal from the HeNB. Accordingly, the UE that is notbeing served by a HeNB does not have to perform complicated control suchas changing a serving cell and can notify a HeNB of the HII with simplecontrol. The UE that has transmitted the PRACH for HII may not berequired to receive a random access response. In addition, the HeNB thathas received the PRACH for HII notification may not transmit a randomaccess response using the PDCCH. This allows the UE that has transmittedthe PRACH for HII to avoid judging a reception failure even when it doesnot receive a random access response. Further, the HeNB that hasreceived the PRACH for the HII can reduce the transmission of a randomaccess response. This alleviates the load of the processes of the UE andHeNB and allows radio resources to be effectively used.

In a case where a UE notifies the HII by mapping it on (or including itin or together with) an RRC establishment request as the method ofnotifying a given HeNB of the HII, an RRC connection establishmentrequest of the RACH procedure used in uplink initial transmission may beused. Transmission is enabled on the MSG3 of the RACH procedure. Thisenables to notify the HII before the RRC connection state is establishedbetween the HeNB and the UE. In the case where the UE that notifies theHIT is in the RRC_Idle state, the state does not need to be changed,which makes the HII notification control simpler.

In a case where the HII is notified by mapping it on the RRC message orin a case where the HII is notified by mapping it on the NAS message,the UE that notifies the HII does not need to change the state whenbeing in the RRC connected state, which makes the HII notificationcontrol simpler.

In a case where the HII is notified using the UL-SCH, in a case wherethe HII is notified by mapping it on the RRC establishment request, in acase where the HII is notified by mapping it on the RRC message, in acase where the HII is notified by mapping it on the NAS message, and inthe case where the HII is notified by MAC signaling, the informationindicating that the signal is the HII may be mapped. This enables a HeNBto distinguish the signal from other signals, and thus can reduce acontrol delay, such as preferentially performing the process foravoiding interference by the HII.

First Modification of Second Embodiment

In the embodiment above, as a specific example of the method of findingthe RACH configuration parameter of a HeNB by a UE, a HeNB notifies amacro cell nearby of the RACH configuration parameter of the own HeNB,and the macro cell notifies a UE being served by the macro cell of theRACH configuration parameter of the HeNB. The present modificationdiscloses another method. A UE obtains the RACH configuration parameterfrom a HeNB present in its vicinity.

FIG. 23 is a conceptual diagram in a case where a UE obtains the RACHconfiguration parameter from a HeNB present in its vicinity. Theportions of FIG. 23 corresponding to those of FIG. 22 are denoted by thesame reference numerals, which are not described. The UE 2207 obtainsthe RACH configuration parameter from the HeNB 2209 present in itsvicinity by means of an air-interface 2301. The method of obtaining theRACH configuration parameter by means of the air-interface 2301 isdisclosed below.

The UE performs measurements of cells nearby and receives the broadcastinformation of the detected cells, to thereby obtain the RACHconfiguration parameters. The method disclosed in the first modificationof the first embodiment may be applied to a series of method up to thereception of the broadcast information. The processes from Step ST1702to Step ST1705 of FIG. 17 are applicable. In Step ST1704, a UE obtainsthe RACH configuration parameter being the broadcast information from acell nearby. In the LTE standard, the RACH configuration parameter isincluded in the SIB2 of the broadcast information. Accordingly, it ispossible to obtain the RACH configuration parameter of the cell byobtaining the SIB2 of the broadcast information. It suffices that the UEassociates the RACH configuration parameter obtained from a cell presentin its vicinity with the PCI of the cell obtained in Step ST1703 andstore those.

It takes time for a UE to obtain the SIB2 of all of the cells detectedin the measurements of cells nearby, and thus, the process of the UEincreases enormously, leading to an increase of power consumption. Inorder to solve this problem, in Step ST1705 of FIG. 17 , the UE mayobtain the cell type information and obtain the SIB2 of only the HeNB,to thereby obtain the RACH configuration parameter. In a case where thePCI of the HeNB can distinguish a cell from a cell of another type, theUE may judge whether or not it is a HeNB from the PCI of the cellobtained in Step ST1703 and obtain the SIB2 of only the HeNB, to therebyobtain the RACH configuration parameter.

Alternatively, in a case of performing measurements upon instructionfrom a serving cell, in Step ST1702, the UE may obtain the SIB2 of thebroadcast information together with the measurement instruction messagefrom the serving cell in advance and specify the cell from which the UEobtains the RACH configuration parameter. The cell may be specifiedusing the PCI or GCI. Alternatively, the measurement instruction messagemay include the information indicating whether or not it is required toobtain the RACH configuration parameter. Still alternatively, at first,the serving cell may be notified of the results obtained by measuringonly the received power, and the serving cell may again notify a UE ofthe cell whose SIB2 should be obtained by the measurement instructionmessage, based on the report of the measurement results. The UE that hasreceived the message receives the broadcast information of the cellagain, and receives the RACH parameter. This enables to reduce theprocesses of a UE and reduce power consumption.

The RACH configuration parameter is configured to be included in theSIB2 in the description above, not limited thereto, and the RACHconfiguration parameter may be configured to be included in another SIBor MIB. Also in this case, similar effects to those in the case wherethe RACH configuration parameter is included in the SIB2 can beobtained.

The method disclosed in the present modification enables a UE to obtainthe RACH configuration parameter from a HeNB present in its vicinity. AHeNB normally broadcasts the RACH configuration parameter for a UE beingserved by the own cell. With the use of the above, it is possible toeliminate exceptional signaling for HII notification, for example,signaling for notification of the RACH configuration parameter of a HeNBfrom a macro cell to a UE. This enables a UE to obtain the RACHconfiguration parameter of a HeNB without increasing a signaling load.In combination with the method of determining, by a UE, a HeNB to benotified, which has been disclosed in the second modification of thefirst embodiment, it is possible to reduce the processes via a macrocell. Accordingly, the signaling load as a system can be reduced andpower consumption can be reduced.

Second Modification of Second Embodiment

In some cases, a cell that is expected to avoid a situation in whichinterference becomes problematic, that is, a cell that is notified ofthe HIT is a CSG cell. At times, a UE present in the vicinity of the CSGcell does not belong to the CSG. In such a case, the UE cannot notifythe HII even when a macro cell tries to notify the CSG cell of the HIIvia the UE. This is because the UE is not allowed to access the CSG cellin a case where the CSG whitelist does not include the CSG-ID of the CSGcell, as described in Non-Patent Document 3 above.

For example, in a case where the HeNB notified of the HII from a macrocell is a CSG cell and a UE nearby does not have the CSG-ID of the CSGcell in the CSG whitelist, the macro cell cannot notify the HeNB of theHII via the UE. Accordingly, the macro cell cannot notify the HeNB of aphysical resource in which interference occurs, and cannot schedule thephysical resource to a UE being served thereby. Alternatively, even in acase where scheduling is performed, the interference from the CSG celldegrades the communication quality. Such a situation reduces thecommunication rate and interrupts the communication at worst.

In order to solve the above-mentioned problem, a UE that does not havethe CSG-ID of a CSG cell in a CSG whitelist may be allowed to access theCSG cell. As described above, however, the CSG cell is a cell used onlyby users belonging to a specific group. Therefore, a case where a UE isallowed to access the CSG cell in every situation is against theobjective of the CSG. Therefore, it is limited to the case of notifyingthe HII. That is, in a case where a UE that does not have the CSG-ID ofa CSG cell in the CSG whitelist notifies the HII, the UE is allowed toaccess the CSG cell. This enables to notify the CSG cell of the HII alsoin a case where there is only a UE that does not belong to the CSG-ID ofthe CSG cell.

In a case of receiving a signal from a UE that does not belong to theCSG-ID, the CSG cell needs to judge whether or not the signal is theHII. Accordingly, the CSG cell does not allow the access from the UE ina case where the signal is not the HII or allows the access from the UEin a case where the signal is the HII.

As the method of judging whether or not the signal from a UE is the HIIby a CSG cell, the method disclosed in the second embodiment may beapplied. In the case of the notification using the PRACH, there may beused a method of partitioning at least any one of the preamble sequenceof the PRACH and physical resources on a frequency-time axis used in thePRACH for one for HII notification and the other for normal PRACH.Alternatively, in a case of the notification using the UL-SCH, in a caseof the notification by being mapped on an RRC establishment request, ina case of the notification by being mapped on an RRC message, and in acase of the notification by being mapped on the NAS message, the methodof mapping the information indicating that the signal is the HII may beused. This enables a CSG cell to judge whether or not the signal from aUE is the HII and, in a case where a UE that does not have the CSG-ID ofthe CSG cell in a CSG whitelist notifies the HII, it can access the CSGcell. Further, also in a case where a cell that is expected to avoid asituation in which interference becomes problematic, that is, a cell tobe notified of the HII is a CSG cell, it is possible to notify the cellof the HII via a UE, which prevents a decrease in communication rate andinterruption of communication.

Third Embodiment

Non-Patent Document 9 proposes the use of the PRACH and UL-SCH as thechannels for notification from a UE to a HeNB as described above, butdoes not describe anything else and does not specifically disclose thestate of a UE that notifies a HeNB of the HII. Whether the UE is in theRRC connected state or RRC_Idle state and the mechanism to, for example,notify the HII in each state are unclear. For example, the PRACH isnormally a channel used in a case when a UE in RRC_Idle starts uplinktransmission, and thus a UE in the RRC connected state that hasestablished the RRC connection cannot use the PRACH. This causes aproblem that the HeNB cannot be notified of the HII via a UE in the RRCconnected state. In order to solve the above-mentioned problem, thepresent embodiment discloses the method of notifying the HII inaccordance with the state of a UE.

In the present embodiment, in a case where a UE in the RRC_connectedstate, that is, in the connected state notifies a HeNB of the HII, theUE changes to the RRC_Idle state, that is, the idle state. Then, the UEnotifies the HeNB of the HII after changing to RRC_Idle.

FIG. 24 is a diagram showing a sequence example of a mobilecommunication system in a case where a UE changes to RRC_Idle and thennotifies a HeNB of the HII. The serving cell is a macro cell. In StepST2401, the UE is in the RRC_connected state.

In Step ST2403, the serving cell that has notified the HeNB of the HIIvia the UE in the RRC_connected state in Step ST2402 notifies the UE inthe RRC_connected state (Step ST2401) of the broadcast informationindicating that the HII is notified or the HII being theinterference-related information. In Step ST2404, the serving cell thathas notified the information indicating that the HII is notified or theHII in Step ST2403 notifies the UE of an RRC connection release message.In Step ST2405, the UE that has received the RRC connection releasemessage releases the RRC connection and changes to the RRC_Idle state.

After changing to RRC_Idle, in Step ST2406, the UE notifies a HeNB to benotified of the HII of the HII. In Step ST2407, the UE that has notifiedthe HII issues the RRC connection request to the serving cell.

In Step ST2408, the RRC connection process is performed between theserving cell that has received the RRC connection request and the UE,whereby the RRC connection is established.

The RRC connection release message of Step ST2404 may be included inStep ST2403. Alternatively, it may be preliminarily determined in astatic manner that the RRC connection is released after the informationindicating that the HII is notified or the HII is notified in StepST2403. This enables to omit the RRC connection release message of StepST2404.

The method disclosed in the second embodiment is applicable to themethod of notifying the HII in Step ST2406. As to a HeNB to be notifiedof the HII or as to whether the own UE notifies a HeNB of the HII, themethod disclosed in the first embodiment is applicable.

In Step ST2407, the UE that has notified the HII issues the RRCconnection request to the serving cell. This enables the UE to performcommunication again while, for example, communication with a servingcell is being performed.

As another method, the UE that has notified the HII in Step ST2406 mayperform cell reselection. This enables to select the best cell havingthe highest received power at that time. In addition, the communicationquality after the notification of the HII can be improved.

After the notification of the HII in Step ST2406, the serving cell mayjudge whether or not the UE issues the RRC connection request orperforms cell reselection for returning to the serving cell, to therebynotify the UE of the judgment. The parameter indicating the above may beprovided so as to be included in Step ST2403 or Step ST2404 to benotified. In a case of being included in the RRC connection release inStep ST2404, the parameter may be added to the cause information of therelease.

In a case of notifying a UE during communication of the HII, the servingcell may take measures for preventing the data from being lost while theUE establishes the RRC connection with the serving cell again. Forexample, the serving cell includes the information indicating that theRRC connection request is issued for returning to the serving cell inStep ST2403 or Step ST2404 and then notifies that information after theUE notifies the HII, and after that, stores the data to be exchangedwith the UE. After the RRC connection process with the UE is performedin Step ST2408, the serving cell communicates the stored data with theUE. Alternatively, the RRC connection request in Step ST2407 may includethe information indicating the RRC connection request after thenotification of the HII. This enables the serving cell to distinguish anormal RRC connection request from the RRC connection request after thenotification of the HIT.

The processes described above enable to prevent the data during thenotification of the HII from being lost even if a UE duringcommunication changes to RRC_Idle, whereby the serving cell is allowedto continuously provide service to the UE.

Accordingly, it is possible to notify a HeNB of the HII via a UE in theRRC_connected state. Further, in a case where a UE that notifies the HIIis in the RRC_connected state, the UE is allowed to notify the HII usingthe PRACH.

If the RACH configuration parameter of the HeNB required in the case ofnotifying the HeNB of the HII in Step ST2406 is obtained in advance bythe method disclosed in the second embodiment, the UE is allowed tonotify the HeNB of the HII at an early stage.

As another method, the UE may perform cell reselection to the HeNB afterchanging to the RRC_Idle state in Step ST2405, and then may notify theHII. It suffices that the UE that has notified the HII after cellreselection to the HeNB performs cell reselection to an original servingcell after the notification of the HII and, in Step ST2407, notifies theRRC connection request.

The cell reselection to a HeNB enables to establish an uplink as well asa downlink for the HeNB. In this case, it is also possible to establishthe RRC connection with the HeNB, which allows the notification of theHII by signaling after the RRC connection establishment.

A UE may obtain the RACH configuration parameter by performing cellreselection to the HeNB and receiving the broadcast information from theHeNB rather than obtaining the RACH configuration parameter in advance.This eliminates the need to obtain the RACH configuration parameter inadvance though a control delay increases.

First Modification of Third Embodiment

In the embodiment described above, a UE is changed to RRC_Idle and thennotifies the HII for notifying a HeNB of the HII via a UE in the RRCconnected state. In the present modification, a UE notifies a HeNB ofthe HII while being in the RRC connected state, as another method. Theserving cell stops scheduling (resource allocation) to the UE while theUE notifies a HeNB of the HII.

A trigger for stopping scheduling to the UE may be a case where aserving cell notifies the UE of the information indicating that the HIIis notified or the HII or a case where a serving cell receives theinformation indicating that the HII is notified from a UE or a signalindicating that the HII has been received.

A trigger for allowing scheduling to the UE again may be a case where ascheduling restart request signal from the UE is received. A schedulingrequest signal may be used as the scheduling restart request signal.Alternatively, the information indicating a scheduling restart requestafter the completion of the HII notification to a HeNB may be includedin a scheduling request signal and notified.

As another method regarding a trigger for allowing scheduling to the UEagain, in a case where a HeNB receives the HII from a UE and thennotifies the serving cell of the information indicating that the HII hasbeen received, a trigger may be the reception of the notification. An S1interface may be used in the notification from the HeNB to the servingcell.

As another method regarding a trigger for allowing scheduling to the UEagain, in a case where a timer for a period in which scheduling to theUE is stopped is provided, a trigger may be the expiration of the timer.The timer may be started by the trigger for stopping scheduling to theUE.

FIG. 25 is a diagram showing a sequence example of a mobilecommunication system in a case where a UE notifies a HeNB of the HIIwhile being in the RRC connected state. The portions of FIG. 25corresponding to those of FIG. 24 are denoted by the same step number,and the processes thereof are not described in detail.

In Step ST2501, the serving cell that has notified a UE of theinformation indicating that the HII is notified or the HII in StepST2403 stops scheduling to the UE. In Step ST2502, the UE that hastransmitted the HII to a HeNB transmits a scheduling request signal tothe serving cell.

In Step ST2503, the serving cell that has received a scheduling requestsignal from the UE in Step ST2502 starts scheduling to the UE.

As described above, the scheduling request signal in Step ST2502 mayinclude the information indicating the scheduling restart request afterthe HeNB has been notified of the HII. In a case where a UE does nottransmit the scheduling restart request signal or in a case where a HeNBdoes not transmit the information that it has received the HII from aHeNB for a certain period, the serving cell may again notify the UE ofthe information indicating that the HII is notified or the HII. A timermay be set as a certain period. This enables a serving cell to notify aHeNB of the HII with reliability, which reliably avoids interference.

It has been described that the method disclosed in the second embodimentis applicable as the method of notifying the HII in Step ST2406. Forexample, it is the method of notifying the HII using the PRACH. Asdescribed in Non-Patent Document 1, however, a case where a UE in theRRC connected state performs the RACH procedure (hereinafter, referredto as a RACH procedure allowed state) is limited. Therefore, in a casewhere a UE in the RRC connected state notifies the HII, the UE has towait for the RACH procedure allowed state. This latency is a delay time,and accordingly, scheduling in which the avoidance of interference isreflected immediately cannot be performed. Further, in a case where theRACH procedure allowed state is not obtained, it is impossible to notifythe HII using the PRACH, and scheduling for avoiding interference cannotbe performed per se.

In order to solve the above-mentioned problem, in a case where a UE inthe RRC_connected state notifies the HII, it is allowed to perform theRACH procedure. Alternatively, in a case where a UE in the RRC_connectedstate notifies the HIT, the transmission of the PRACH is allowed.

This allows a UE in the RRC_connected state that has received the HII orthe information indicating that the HII is notified from a serving cellto notify a HeNB of the HII using the RACH procedure or PRACH. Thisenables a UE to notify a HeNB of the HII with a small delay time.

The method disclosed in the present modification enables to notify aHeNB of the HII via a UE in the RRC_connected state. Further, it ispossible to prevent a UE from changing to the RRC_Idle state, wherebythe UE can notify a HeNB of the HII immediately after receiving the HIIor the information indicating that the HII is notified. Accordingly, thetime period required for control to notify the HII can be reduced. Thisenables scheduling in which an interference situation at a certain timeis immediately reflected with a small control delay.

Further, the RRC connection is established between a serving cell (macrocell) and a UE after the UE notifies the HII, whereby the UE is allowedto communicate with the serving cell again. It is not required toperform the RRC connection process on this occasion, which enablescommunication with fewer processes at an early stage. This leads to areduction in control delay and lower power consumption of a UE.

While a serving cell stops scheduling to a UE in the method above, onlyuplink scheduling may be stopped. The UE requires uplink transmissionfor notifying a HeNB of the HII. It is possible to prevent this uplinktransmission from being performed simultaneously with the uplinktransmission scheduled from the serving cell.

Further, a serving cell may avoid using a subframe in which a physicalresource for PRACH transmission of a HeNB is present in scheduling to aUE, rather than stop scheduling to a UE. That is, the serving cellavoids allocating the subframe in which the physical resource is presentto a UE. Similarly, this enables to prevent the uplink transmission frombeing performed simultaneously.

There may be used a radio frame in which a physical resource for PRACHtransmission of a HeNB is present, not a subframe. Similar effects canbe achieved also in this case.

The serving cell recognizes the physical resource for PRACH transmissionof a HeNB in advance. The method disclosed in the second embodiment maybe used as this method. This allows the serving cell to performscheduling to a UE while avoiding the subframe in which a physicalresource is present or a radio frame.

Similarly, in the scheduling to a UE, the serving cell may avoid the useof a subframe in which a physical resource for UL-SCH that is allocatedto a UE by a HeNB or a radio frame. Likewise, a UE can avoid uplinktransmission simultaneously. It suffices that a HeNB notifies thephysical resource information to which UL-SCH is allocated as in themethod of notifying a cell nearby of the RACH configuration disclosed inthe second embodiment.

In performing semi-persistent scheduling, the serving cell may avoid theuse of a subframe in which a physical resource for PRACH transmission ofa HeNB is present. Alternatively, the serving cell may avoid the use ofa subframe in which a physical resource for UL-SCH that is allocated toa UE by a HeNB is present. There may used a radio frame, not a subframe.It suffices that a HeNB notifies the physical resource informationallocated in semi-persistent scheduling as in the method of notifying acell nearby of the RACH configuration disclosed in the secondembodiment. Similarly, a UE can avoid performing uplink transmissionsimultaneously.

In a case where a UE is in the state in which a bearer for a dedicatedcontrol channel is disconnected between a serving cell and the UE or theradio link failure state when the UE notifies a HeNB of the HII, in StepST2502, the UE may use an RRC reconnection request message, not ascheduling request. After performing the RRC reconnection processbetween a UE and a serving cell, the serving cell may perform schedulingto a UE as required.

The serving cell stops scheduling to a UE in the method described above,but in a case where the scheduling is not stopped and the subframe fortransmission of the HII to a HeNB overlaps the subframe for uplinktransmission to a macro cell at the UE, the UE may preferentiallyperform any one of them. For example, a UE gives priority to uplinktransmission to a serving cell and does not transmit the HII to a HeNB.This enables a UE to avoid simultaneous transmission as well as aninterruption of the communication with a serving cell.

On the contrary, for example, a UE may give priority to transmission ofthe HII to a HeNB and avoid uplink transmission to a serving cell. Thisenables the UE to avoid simultaneous transmission as well asinterference owing to the transmission of the HII. Further, though theserving cell cannot receive uplink transmission from a UE, it may causethe UE to perform uplink transmission again through retransmissioncontrol of HARQ and ARQ. This causes a delay but does not interrupt thecommunication.

The serving cell may select a UE to which uplink scheduling is notperformed and notify a HeNB of the HII via the UE without stoppingscheduling to a UE. For example, it suffices that in a case of listingUEs to be notified of the HII in the HII notified HeNB list byassociating those with a HeNB, a macro cell may list a plurality of suchUEs. For example, the macro cell may number UEs in decreasing order ofreceived power and list a plurality of UEs. In a case where a servingcell has performed uplink scheduling to a UE with the highest receivedpower from the HeNB, in notifying a HeNB of the HII, the serving cellmay notify a HeNB of the HII via a UE in the second order. This methodenables a UE to avoid uplink transmission simultaneously.

Second Modification of Third Embodiment

In the present modification, as another method of notifying a HeNB ofthe HII via a UE in the RRC_connected state, a serving cell causes theUE to notify the HII using handover (HO) to the HeNB.

A serving cell takes a HeNB to be notified of the HII as a target cell,and activates a HO procedure for a UE that should notify the HeNB of theHIT. On this occasion, the HO procedure may be activated by a pluralityof UEs, and preferably, by one. This is because a signaling load for HOto a HeNB increases considerably if a plurality of UEs activate the HOprocedure. The method disclosed in the first modification of the firstembodiment is applicable as the method of limiting the number of UEsthat activate the HO procedure to one.

A UE performs RRC establishment for a HeNB instructed by a network(serving cell), using the procedure of normal HO. The UE notifies theHII in performing RRC establishment. As described above, the UE may usethe PRACH or RRC establishment request message. Alternatively, the UEmay notify the HII after the RRC establishment with a HeNB in accordancewith the HO procedure. This enables the notification by the MAC message,RRC message or NAS message.

In a case where the HII is notified in performing RRC establishment, theHeNB that has received the HII causes a UE to change back to an originalserving cell, that is, returns a UE under control of the originalserving cell. As the method for this, it suffices that the HeNB that hasreceived the HII does not end the RACH procedure or notifies a UE of thereject message for the RRC establishment request message. As a result, aUE performs the process considering that it has failed in HO, and thusperforms the process of changing back to an original serving cell. Inchangeback, the UE may perform RRC establishment again for an originalserving cell using the RRC reconnection request message.

In a case where a UE does not perform RRC connection with a HeNB andperforms the process of changing back to an original serving cell, aserving cell may avoid a HO request or the notification of data and theinformation related to the data such as a data number (data forwarding,SN status transfer). This enables to reduce a signaling amount between aserving cell and a HeNB. Alternatively, a serving cell may hold theinformation related to the data and, after the RRC reconnectionestablishment with the UE, may communicate the data with the UE. Thisenables to continue communication between a serving cell and a UE.

In a case where the HII is notified after the RRC establishment with aHeNB, the HeNB causes the UE to perform HO to an original serving cellas a target cell. This enables a UE to perform communication again afterperforming HO to an original cell.

The method disclosed in the present modification enables to notify aHeNB of the HII via the UE in the RRC connected state. The serving cellmay notify a UE of the RACH configuration parameter of a HeNB as anormal HO procedure, and is not required to make notification inadvance. This enables to reduce a signaling load.

Third Modification of Third Embodiment

The third embodiment to the second modification of the third embodimenthave disclosed the method of notifying a HeNB of the HII via a UE in theRRC_connected state. The present modification discloses an example ofthe method of notifying a HeNB of the HII via a UE in the RRC_Idlestate.

Normally, a serving cell does not instruct measurements to a UE in theRRC_Idle state. Accordingly, a UE in the RRC_Idle state may use themethod of regularly measuring a surrounding radio wave environment,which has been disclosed in the first modification of the firstembodiment.

It suffices that the serving cell notifies a UE being served thereby ofthe information indicating whether or not a HeNB is deployed in thecoverage of the own serving cell. As a result, in a case of a servingcell that has no HeNB deployed in the coverage thereof, a UE does notneed to perform measurement regularly in the RRC_Idle state, leading tolower power consumption.

The notification of the information indicating whether or not a HeNB isdeployed in the coverage may be broadcast as the broadcast informationand, for example, may be included in the SIB1. The transmission timingof the SIB1 is determined in advance, which allows a UE to receive theSIB1 at an early stage.

The UE that has received the information indicating whether or not aHeNB is deployed in the coverage measures a surrounding radio waveenvironment, irrespective of the received power of a serving cell. Thesurrounding radio wave environment is measured in cycles. The cycle maybe preliminarily determined in a static manner or may be mapped on thebroadcast information to be broadcast from the serving cell.

Alternatively, a serving cell may notify a UE being served thereby of apath loss (or range of a path loss) to the HeNB deployed in the coverageof the own serving cell. It suffices that the path loss to each HeNB isbroadcast as the broadcast information, which may be included in, forexample, the SIB4. The neighbor cell information is mapped on the SIB4,and thus, the path loss may be associated with the neighbor cellinformation to be notified.

The UE that takes a cell to which the path loss is broadcast as aserving cell may derive a path loss from a serving cell and performmeasurements while that path loss is identical to the path loss to theHeNB (or in a specific range).

The method disclosed in the eighth modification of the first embodimentmay be used as the method of notifying, by a serving cell, a UE in theRRC_Idle state of the indication that the HII or the HII is notified.

The method involving the use of the PRACH or the method involving theuse of the RRC connection request disclosed in the second embodiment maybe used as the method of notifying a HeNB of the HII by a UE in theRRC_Idle state. The use of the above-mentioned method enables to notifya HeNB of the HII via a UE in the RRC_Idle state. This enables to notifya HeNB of the HII without a UE during communication (during RRCconnection establishment) in some cases. Therefore, it is possible toprevent a delay in data transmission for the UE during communication.

Fourth Embodiment

The HeNB that has received the HII performs scheduling for avoidinginterference with a macro cell in accordance with the contents of theHII, such as avoiding allocation to a physical resource or reducing thepower of the physical resource. However, the macro cell may have alreadybeen in a situation in which the physical resource is not used at timesand, if the scheduling for avoiding interference continues, the useefficiency of a physical resource decreases. Non-Patent Document 9 doesnot disclose this problem as described above. Accordingly, in thepresent embodiment, the HeNB that has received the HII releases thescheduling for avoiding interference at a predetermined time for solvingthis problem.

As the method for releasing the scheduling for avoiding interference bythe HeNB that has received the HII, the scheduling period for avoidinginterference is set. Specifically, a timer for the period is provided,and the scheduling for avoiding interference is released upon expirationof the timer.

FIG. 26 is a diagram showing a sequence example of a mobilecommunication system in a case where a timer is provided for releasingthe scheduling for avoiding interference by a HeNB. The portions of FIG.26 corresponding to those of FIG. 24 are denoted by the same stepnumbers, and the processes thereof are not described in detail. Themethod disclosed in the third embodiment is used as the method ofnotifying the HII in the present embodiment, which may be anothermethod.

In Step ST2701, the HeNB that has received the HII from the UE in StepST2406 starts scheduling for avoiding interference to a UE being servedby the own cell (HeNB) in accordance with the HII. In this case, a timerfor setting a period until the scheduling for avoiding interference isreleased is provided, and the timer is started. The timer starts at thetime at which, for example, the HII is notified, and clocks a lapse ofthe period predetermined as a period from the notification of the HII tothe release of scheduling for avoiding interference.

In Step ST2702, the HeNB judges whether or not the timer has expiredand, in the case where the timer has not expired, continues schedulingfor avoiding interference and checks whether or not the timer hasexpired. In the case where the timer has expired, the HeNB moves to StepST2703.

In Step ST2703, the HeNB releases the scheduling for avoidinginterference to the UE being served thereby. In this case, the timer isreset. This enables the HeNB to perform normal scheduling to a UE beingserved thereby. As a result, the HeNB does not continue the schedulingfor avoiding interference indefinitely, which prevents a decrease in useefficiency of a radio resource.

First Modification of Fourth Embodiment

As another method for releasing the scheduling for avoiding interferenceby the HeNB that has received the HII, an HII release signal is notifiedto the HeNB. The HeNB releases the scheduling for avoiding interferencewhen receiving the HII release signal.

FIG. 27 is a diagram showing a sequence example of a mobilecommunication system in a case where the HeNB releases the schedulingfor avoiding interference in a case of receiving the HII release signal.The portions of FIG. 27 corresponding to those of FIG. 24 are denoted bythe same step numbers, and processes thereof are not described indetail. The method disclosed in the third embodiment is used as themethod of notifying the HII in the present modification, which may beanother method.

In Step ST2801, the HeNB that has received the HII from a UE in StepST2406 starts the scheduling for avoiding interference for a UE beingserved by the own cell (HeNB) in accordance with the HII.

In a case where the serving cell is in a situation in which thescheduling for avoiding interference may be released for the HeNB, forexample, in a situation in which the scheduling to the physical resourcenotified by the HII is not required for the UE being served thereby, inStep ST2802, the serving cell activates the procedure for releasing theHII.

In Step ST2803, the serving cell notifies the UE of the informationindicating that the HII is released. In Step ST2804, the serving cellnotifies the UE of an RRC connection release message.

In Step ST2805, the UE that has received the information indicating thatthe HII is released in Step ST2803 and received an RRC connectionrelease message in Step ST2804 changes to RRC_Idle.

In Step ST2806, the UE notifies a HeNB to be notified of the informationof the information indicating that the HII is released. In Step ST2809,the HeNB that has received the information indicating that the HII isreleased releases the scheduling for avoiding interference for a UEbeing served thereby. In Step ST2807, the UE that has notified the HeNBof the information indicating that the HIT is released in Step ST2806transmits an RRC connection request signal to the serving cell and, inStep ST2808, performs the RRC connection process between the servingcell and the UE. It suffices that the method of notifying theinformation indicating that the HII is released is similar to that inthe case where the HII is notified. On this occasion, the UE thatnotifies the HII may be different from the UE that notifies theinformation indicating that the HII is released.

As described above, the HeNB is notified of the information indicatingthat the HII is released, and thus the HeNB does not continue thescheduling for avoiding interference indefinitely, which prevents adecrease in use efficiency of a radio resource. In addition, whether theserving cell releases the HII can be judged in this method, whichenables a serving cell to flexibly perform appropriate scheduling to aUE being served thereby.

Fifth Embodiment

The second embodiment and fourth embodiment have disclosed the method ofnotifying a HeNB of the HII by a UE using the RACH configuration of theHeNB. The present embodiment discloses the method of notifying a HeNB ofthe HII by a UE using the RACH configuration of the serving cell, as aspecific mechanism in which a macro cell notifies a HeNB of the HIT viaa UE.

FIG. 28 is a conceptual diagram in a case where a UE notifies a HeNB ofthe HII using the RACH configuration of the serving cell. The portionsof FIG. 28 corresponding to those of FIG. 22 are denoted by the samereference numerals, which are not described. In FIG. 28 , an arrow 2601shows that the HeNB 2209 receives the PRACH 2206 transmitted from the UE2207 to the eNB 2204 being a macro cell.

In the case of notifying the HeNB 2209 of the HII, the macro cell 2204notifies the HeNB 2209 of the HII via the UE 2207 being served by theown macro cell 2204. For example, the UE 2207 that has been notified ofthe indication that the HII is notified from the macro cell 2204 to theHeNB 2209 or the HII by the methods disclosed in the first embodiment tothe eighth modification of the first embodiment transmits the HII to theHeNB 2209.

The UE 2207 notifies the HII using the PRACH 2206 by the RACHconfiguration of the macro cell 2204. The HeNB 2209 receives the PRACH2206, to thereby receive the HII. This enables the macro cell 2204 tonotify the HeNB 2209 of the HII via the UE 2207 being served thereby.

Normally, a UE being served by a macro cell recognizes the RACHconfiguration of the macro cell for starting communication with themacro cell. The UE receives the broadcast information broadcast from themacro cell, to thereby obtain the RACH configuration parameter.Accordingly, the UE being served by the macro cell can transmit thePRACH to the macro cell using the RACH configuration of the macro cell.However, the HeNB normally cannot receive the PRACH transmitted from theUE to the macro cell. This is because the HeNB does not recognize theRACH configuration parameter of the macro cell being a serving cell. Thepresent embodiment discloses below a specific example of the method ofrecognizing the RACH configuration parameter of the macro cell by aHeNB.

The macro cell notifies a HeNB of the RACH configuration parameter ofthe own cell. An S1 interface may be used in the notification. As aspecific example, the macro cell 2204 notifies the HeNB 2209 of the RACHconfiguration parameter of the macro cell using the interface 2210 ofFIG. 28 . An S1 interface is used as the interface 2210. The macro cell2204 may notify the PCI of the own cell together with the RACHconfiguration parameter. It suffices that the HeNB 2209 that hasreceived the RACH configuration parameter associates the PCI of themacro cell 2204 with the RACH configuration parameter and stores those,and may store those in the EPC communication unit 901, protocolprocessing unit 903 or control unit 911 shown in FIG. 9 .

As an example, the method of notifying, by a macro cell, a HeNB deployedin the coverage of the own cell of the RACH configuration parameter isdisclosed. The method disclosed in the first embodiment may be used asthe method of recognizing, by a macro cell, a HeNB deployed in thecoverage of the own cell. For example, the operation of Step ST1401 toStep ST1408 of FIG. 14 may be used.

The macro cell recognizes a HeNB deployed in the coverage of the owncell, and then notifies the HeNB of the RACH configuration parameter ofthe own cell. For example, after the processes of the Step ST1407 andStep ST1408 of FIG. 14 are performed, the macro cell notifies the HeNBin the HII notified HeNB list of the RACH configuration parameter. Themacro cell may notify an added HeNB of the RACH configuration parameter.The macro cell may instruct a deleted HeNB to delete the RACHconfiguration parameter that has been notified or notify the deletedHeNB of the information indicating allowance. This enables a macro cellto notify a HeNB deployed in the coverage of the own cell of the RACHconfiguration parameter of the own cell.

As an example, the method of notifying, by a macro cell, a HeNB deployedin the coverage of the own cell of the RACH configuration parameter isdisclosed, not limited thereto, and an own macro cell (eNB) may notify aHeNB deployed in a certain range of the RACH configuration parameter. Asthe method for this, the modification of the first embodiment may beused. Alternatively, a macro cell may notify a HeNB to be notified ofthe HII of the RACH configuration parameter. As a result of limiting toa certain range or a HeNB to be notified of the HII, it is possible toreduce the signaling load between the macro cell and the HeNB.

The UE that has received the indication that the HII is notified or theHII from the serving cell being a macro cell notifies the HII using theRACH configuration parameter of the serving cell that has been obtainedby receiving the broadcast information of the serving cell. In thiscase, the UE notifies the serving cell of the HII. The method disclosedin the second embodiment may be used as the method of notifying the HIIfrom a UE. The HeNB that has received the RACH configuration parameterfrom the macro cell receives the PRACH from the UE in accordance withthe RACH configuration. The HeNB may receive the PRACH in accordancewith only the configuration used in the HII of the RACH configuration ofthe macro cell. Alternatively, it may be set such the macro cellnotifies the HeNB of only the RACH configuration used in the HII andthat the HeNB receives the PRACH in accordance with only the RACHconfiguration used in the notified HII. Accordingly, in a case where aUE transmits the HII using the PRACH of the RACH configuration of aserving cell being the macro cell, a HeNB is allowed to receive the HIIfrom the UE.

The method as disclosed in the present embodiment enables a macro cellto notify a HeNB of the HII via a UE. The UE notifies the HII using theRACH configuration parameter of the serving cell, and accordingly is notrequired to recognize a HeNB to be notified of the HII. Therefore, theserving cell does not need to notify a UE of the information on a HeNBto be notified of the HII. Alternatively, in a case where a UE selects aHeNB to be notified of the HII, the UE does not need to perform theselection process. This reduces a signaling load and reduces powerconsumption of a UE.

A macro cell can determine the RACH configuration used in thenotification of the HII, which makes scheduling of a UE for notifyingthe HII easier. For example, in a case where the HII is notified while aUE is in the RRC connected state, which has been disclosed in the firstmodification of the third embodiment, a serving cell can control thescheduling to a UE being served thereby as well as the RACHconfiguration for notifying the HII. Accordingly, the serving cell canbe controlled easily so as not to simultaneously perform scheduling to aUE to be notified of the HII.

Typically, a user equipment receives downlink transmission of a basestation and, based on this, synchronizes to the frequency of the basestation. This function is referred to as automatic frequency control(AFC). In the present embodiment, a UE transmits the PRACH for HIInotification to a serving cell, and accordingly synchronizes to thefrequency of the serving cell. In some cases, the frequency to be usedslightly varies between the serving cell and the HeNB. In such a case,it is difficult for a HeNB to receive the uplink transmission from theUE synchronized to the frequency of the serving cell.

In order to solve this problem, in the present embodiment, a UE uses theuplink carrier frequency of the HeNB for the uplink transmission fornotifying the HII. In order to perform the AFC for the downlinktransmission from a HeNB, a UE measures cells nearby, receives thedownlink transmission from the HeNB to be notified of the HII, andperforms the AFC. The measurements of cells nearby may be performedregularly or performed in a case where the indication that the HII isnotified or the information of the HII is received from the servingcell. In this case, it suffices that the serving cell notifies a UE ofthe HeNB information that the UE is notified of the HII.

In a case where a UE selects a HeNB to be notified of the HII, theserving cell does not need to notify the HeNB information that the UE isnotified of the HII. As a result, even in a case where the carrierfrequency to be used slightly varies between a serving cell and a HeNB,if a UE notifies the HII using the uplink transmission of a servingcell, the HeNB can receive the HII.

First Modification of Fifth Embodiment

The present modification discloses another specific example forrecognizing the RACH configuration parameter of a macro cell by a HeNB.The HeNB receives the broadcast information of a macro cell nearbythrough measurements and obtains the RACH configuration parameter. Asthe method for this, the method disclosed in the first embodiment may beused. The first embodiment has disclosed that in power-on orinitialization, or while the transmission is stopped, a HeNB measures asurrounding radio wave environment, measures the received power of acell present in its vicinity, and obtains the cell identity (PCI) of thecell, to thereby detect a cell. In addition, the first embodiment hasdisclosed that a HeNB receives the broadcast information of the detectedcell. On this occasion, the HeNB may obtain the RACH configurationparameter of the cell included in the broadcast information of the cell.The RACH configuration parameter is normally included in the SIB2. Itsuffices that the HeNB receives the SIB2 to obtain the RACHconfiguration parameter.

The configuration as described above enables a HeNB to obtain the RACHconfiguration parameter of a cell present in its vicinity or a macrocell. This method eliminates the need to notify, by a macro cell, a HeNBof the RACH configuration parameter by means of the S1 interface. Thisenables to reduce the signaling load of the S1 interface. As a result ofthe HeNB having the function of measuring a surrounding radio waveenvironment, function of detecting a cell, function of receiving thebroadcast information of the cell, and function of obtaining thebroadcast information, the HeNB can obtain the RACH configurationparameter from a macro cell as well.

Second Modification of Fifth Embodiment

In the fifth embodiment described above, in a case where the carrierfrequency to be used slightly varies between a serving cell and a HeNB,a UE uses the uplink carrier frequency of the HeNB in the uplinktransmission for notifying the HII. In the present modification, asanother method, a UE uses the uplink carrier frequency of the servingcell in the uplink transmission for notifying the HII.

The HeNB has to receive the HII with the uplink frequency from a macrocell being the serving cell. In order to achieve this, the HeNB performsthe AFC for the downlink transmission of the macro cell and receives theHII with the uplink frequency of the macro cell. The HeNB may take themacro cell notified of the RACH configuration parameter as the macrocell for which the AFC is performed.

The HeNB performs measurements of cells nearby based on the PCI of themacro cell for which the AFC is performed, and receives the downlinktransmission of the macro cell having the PCI. The measurements of cellsnearby may be performed regularly or performed in a case where the RACHconfiguration parameter is received from a cell nearby. As a result, ina case where a UE notifies the HII using the uplink transmission of theserving cell, a HeNB can receive the uplink transmission for HIInotification even when the carrier frequency to be used slightly variesbetween the serving cell and the HeNB.

The RACH configuration parameter has been described in the fifthembodiment and the modification thereof, not limited to the RACHconfiguration parameter, which may be a parameter for performing uplinktransmission for a serving cell by a UE as in the second embodiment.

Sixth Embodiment

The present embodiment discloses the method of determining the initialtransmission power of the PRACH in a case where the PRACH is used fornotifying a HeNB of the HII.

Non-Patent Document 11 defines the initial transmission power of thePRACH as expressed by Equation (1) below.

PPRACH=min{Pcmax,PREAMBLE_RECEIVED_TARGET_POWER+PL} [dBm]  (1)

In Equation (1), “PL” represents a path loss. “Pcmax” of Equation (1) isdetermined by Equation (2) below, and “PREAMBLE_RECEIVED_TARGET_POWER”of Equation (1) is defined as expressed in Equation (3) below (seeChapter 5.1.3 of TS36.321 V.9.1.0 (hereinafter, referred to as“Non-Patent Document 12” by 3GPP).

Pcmax=min{Pemax,Pumax}  (2)

In Equation (2), “Pemax” is a value that is set per cell and broadcastto a user equipment being served thereby, and “Pumax” is determined fromthe capability of a user equipment.

PREAMBLE_RECEIVED_TARGET_POWER=preambleInitialReceivedTargetPower+DELTA_PREAMBLE+(PREAMBLE_TRANSMISSION_COUNTER−1)*powerRampingStep  (3)

In Equation (3), “preambleInitialReceivedTargetPower” is a part of theRACH configuration, and “DELTA_PREAMBLE” is determined based on thepreamble format (sequence) (see Chapter 7.6 of Non-Patent Document 12).The preamble format (sequence) is a part of the RACH configuration.“PREAMBLE_TRANSMISSION_COUNTER” represents how many times the preambletransmission has been performed. “powerRampingStep” is a part of theRACH configuration, and “*” represents multiplication “×” (seeNon-Patent Document 10).

Non-Patent Document 9 discloses the following. It is disclosed thatbased on the measurement value of the downlink received quality of aHeNB by a UE, a serving cell notifies the user equipment of the uplinktransmission power required for notification of the HII by the UE, orthe UE deduces the required uplink transmission power.

However, in a case where the equations disclosed in Non-Patent Document11 are used for the method of determining the initial transmission powerof the PRACH for HII notification, in a case where the serving cellderives the initial transmission power of the PRACH using thoseequations, and in a case where a UE derives the initial transmissionpower of the PRACH using those equations, “PL” of Equation (1) and“Pemax” of Equation (2) become indeterminate, leading to a problem thatthe initial transmission power of the PRACH cannot be determined.

The present embodiment discloses the method for solving this problem.First, the solution for “Pemax” of Equation (2) is disclosed. A HeNBnotifies a node nearby of “Pemax” of the own cell by means of the S1interface, similarly to the RACH configuration parameter disclosed inthe second embodiment. This enables a serving cell to recognize “Pemax”of the HeNB to be notified of the HII.

In a case where a UE derives the initial transmission power of thePRACH, the serving cell notifies a UE being served thereby of theparameter by a method similar to that of the RACH configurationparameter disclosed in the second embodiment. This allows a userequipment that transmits the PRACH for HII to find “Pemax” of the HeNBto be notified of the HIT. The user equipment determines the initialtransmission power of the PRACH for HII of the HeNB to be notified ofthe HII, using the “Pemax”.

The method involving the use of “Pemax” of the HeNB to be notified ofthe HII for deriving the initial transmission power of the PRACH for HIIhas been disclosed above. However, “Pemax” is used for causing a UEbeing served by a cell that sets “Pemax” to derive the initialtransmission power of the PRACH. That is, “Pemax” is set for a UEpresent in the coverage of the cell.

The present invention has disclosed the method of notifying a HeNB ofthe HII via a UE being served by a macro cell. In this method, a UE isserved by a macro cell and is not served by a HeNB. Therefore, the UEthat notifies the HII is not present in the coverage of a HeNB in somecases. In a case where such a UE uses the initial transmission power ofthe PRACH derived using “Pemax”, there arises a problem that sufficienttransmission power is not achieved and the PRACH cannot be received atthe HeNB.

Accordingly, not “Pemax” but a value (for example, Pemax_a) larger than“Pemax” may be set, to thereby derive the initial transmission power ofthe PRACH. The Pemax_a may be preliminarily determined in a staticmanner or may be broadcast from a serving cell as the broadcastinformation. The serving cell or UE may substitute the Pemax_a for“Pemax” of Equation (2) above.

A new parameter PHIIoffset may be provided for setting an appropriatevalue larger than “Pemax”. Pemax (per HeNB)+PHIIoffset may besubstituted for “Pemax” of Equation (2) above. The PHIIoffset may bepreliminarily determined in a static manner, may be determined by aserving cell, or may be determined by a UE. In a case where it isdetermined by a serving cell, the serving cell may broadcast theparameter to a UE being served thereby by the broadcast information ormay notify the parameter individually. A UE may be notified in a similarmethod to that for the indication that the HII is notified or the HII,which has been disclosed in the first embodiment. Accordingly, it ispossible to take “Pemax” per HeNB into account, which enables to dealwith the case where the coverage varies from HeNB to HeNB.

Further, it is possible to set PHIIoffset suitable for a HeNB to benotified of the HII and a UE to be notified of the HII. For example, ina case where the UE having the highest received power from the HeNB tobe notified of the HII is notified of the HII, it suffices that a valueas small as possible is set in the PHIIoffset. The setting of PHIIoffsetin this manner prevents an increase of uplink transmission power evenwhen there are a large number of UEs to be notified of the HII, whichenables to reduce the uplink interference.

In a case of the method of notifying the HII via a UE present in aspecific received power range from a HeNB, which has been disclosed inthe sixth modification of the first embodiment, the PHIIoffset may bederived with the HeNB range threshold. A correspondence may bedetermined in advance by a predetermined function or in a table.PHIIoffset may be derived by a serving cell that is a macro cell or, inthe case where a UE recognizes the HeNB range threshold, may be derivedby a UE. In this case, the HeNB range threshold may be used directlywithout using the PHIIoffset parameter, to thereby calculate a valuesubstituted for “Pemax” of Equation (2) above. This enables to preventthe transmission of the HII with unnecessary transmission power by a UEin a case where the HII is notified via a UE present in a specificreceived power range from HeNB.

The PHIIoffset may be zero or a negative value, not only a positivevalue. For example, in a case where a HeNB is a CSG cell, a UE that doesnot belong to the CSG-ID of the CSG cell cannot take the CSG cell as aserving cell and takes a macro cell as a serving cell even when beingwithin the coverage of the CSG cell. Therefore, it is possible to causea CSG cell to notify the HII via a UE present in the coverage of the CSGcell, with the PHIIoffset set to zero or a negative value. This enablesto keep the transmission power for HII notification low, achieving areduction in interference and a reduction in power consumption of a UE.

Next, a solution for “PL” of Equation (1) above is disclosed. A userequipment uses the path loss of a serving cell. This allows a userequipment that transmits the PRACH to confirm “PL”. The user equipmentderives the initial transmission power of the PRACH for HII using this“PL”. A UE is allowed to derive the initial transmission power of thePRACH for HII by a typical PL deriving method. However, in a case wherea user equipment uses the path loss of a serving cell in a case ofdetermining the initial transmission power of the PRACH for HII, theinitial transmission power of the PRACH increases unnecessarilydepending on the location of the user equipment, leading to a problemthat unnecessary uplink interference occurs or the power consumption ofa UE increases. Therefore, three specific examples of the method ofdetermining the value of “PL” used in a case of determining the initialtransmission power of the PRACH for HII are disclosed below.

(1) A static value is determined in advance. As a specific example, itis determined in accordance with the standards.

(2) A value is set as a fixed value per HeNB. Each HeNB notifies a macrocell nearby of the fixed value as the RACH configuration parameter. Eachmacro cell notifies a user equipment being served thereby. Two specificexamples of the method of notifying a user equipment are disclosedbelow:

(2-1) notification is made using the broadcast information.

(2-2) notification is made using the dedicated information.

(3) A UE derives the path loss per HeNB in measurements. For example, asdisclosed in the first modification or fourth modification of the firstembodiment, it may be derived through the processes from Step ST1703 toStep ST1705 of FIG. 17 . This prevents the initial transmission power ofthe PRACH for HII from increasing more than necessary. As a result, itis possible to prevent the occurrence of uplink interference or anincrease in power consumption of a UE.

A UE derives the initial transmission power of the normal PRACH usingEquation (1) to Equation (3) above disclosed in Non-Patent Document 11,and derives the initial transmission power of the PRACH for HII usingthe method disclosed in the present embodiment. This allows a macro cellto properly keep the initial transmission power of the PRACH used in thecase of notifying a HeNB of the HII via a UE being served thereby.Accordingly, the HII reception error can be reduced, which enables toprevent the occurrence of uplink interference or an increase in thepower consumption of a UE.

The methods disclosed in the first embodiment to the sixth embodimentmay be appropriately used in combination. This enables the method ofnotifying a HeNB of the HII via a UE in accordance with the situation.Also in the case where a large number of HeNBs will be deployed or inthe case where those are deployed by a general user, the interferencebetween a macro cell and a HeNB can be reduced, which enables to providehigh-speed and high-capacity communication.

The first embodiment to the sixth embodiment have described the HII, butnot limited to the HII, which may be the interference-relatedinformation that is the information related to the interference to aphysical resource used in a macro cell, specifically, a signal foravoiding interference. For example, it may be the OI. The use of themethods disclosed in the first embodiment to the sixth embodimentenables to avoid the interference between a macro cell and a HeNB.

While the first embodiment to the sixth embodiment have disclosed thatan S1 interface is used for transmission of the information between amacro cell and a HeNB, an X2 interface may be used in a case where theX2 interface is provided.

The first embodiment to the sixth embodiment have described the RACHconfiguration parameter, not limited thereto, which may be a parameterfor performing uplink transmission.

While it has been disclosed that the PRACH is used for HII notification,an uplink channel dedicated to HII notification may be newly provided,so that the HII information and HII release information may be notifiedusing the HII notification dedicated uplink channel.

Three specific examples of the HII notification dedicated channel aredisclosed below.

(1) The resource in which uplink transmission of the channel is allowedis discrete from a user equipment in time. Accordingly, a HeNB receivesthe channel, where successive reception is not required anddiscontinuous reception is only required. The HeNB receives the HII, andthus an increase of power consumption is prevented, which is effective.

(2) The resource in which the transmission of the channel is allowed hasa cycle in time. This eliminates the need to notify a resource in whichthe frequent transmission to a user equipment is allowed. Accordingly,an effect that radio resources can be effectively used is obtained.

(3) The frequency allocation of a resource in which the transmission ofthe channel is allowed is determined. This alleviates the load of theprocesses of a user equipment and a HeNB.

The HII notification dedicated channel and configuration thereof may bepreliminarily determined in a static manner. In a case where a UEnotifies a HeNB to be notified of the HII of the HII, the UE notifiesevery HeNB of the HII using the HII notification dedicated channel. Thisenables to simplify the control of a UE. Further, signaling of theconfiguration of the HII notification dedicated channel is not required,which enables to construct a mechanism for notifying the HII withoutincreasing a signaling load.

The first embodiment to the sixth embodiment have disclosed the methodof notifying the interference-related information that is theinformation related to the interference to a physical resource such asthe HII or OI, specifically, a signal for avoiding interference. Thephysical resource may be a component carrier, not a physical resourceblock. For example, in a case where a macro cell performs carrieraggregation, the macro cell provides a signal for avoiding interferencethat includes the information indicating one or a plurality of componentcarriers that are susceptible to interference or are desirably notinfluenced by the interference, and then notifies a HeNB in whichinterference becomes problematic of the signal. The HeNB that hasreceived the signal tries not to interfere by, for example, avoidingscheduling the component carriers to UEs being served thereby, reducingthe power of the component carriers, or avoiding carrier aggregation ofthe component carriers. This allows a macro cell to schedule thecomponent carriers to UEs being served thereby, increase the power ofthe component carriers, or perform carrier aggregation of the componentcarriers. The methods disclosed in the first embodiment to the sixthembodiment may be used for the method of notifying a signal for avoidinginterference and the method of determining the transmission power.

In carrier aggregation, one or a plurality of component carriers thatare allowed scheduling, or one or a plurality of component carriers forwhich scheduling is activated are deployed as one set in some cases. Insuch a case, it is possible to avoid interference on a component carrierbasis by adding, deleting or exchanging component carriers in the setbased on the signal for avoiding interference.

In a case where interference is avoided on a component carrier basis,control may be made such that a macro cell notifies a HeNB of the signalfor avoiding interference in a semi-static manner. While the firstembodiment to the sixth embodiment have disclosed the method ofnotifying a signal for avoiding interference via a UE, notification maybe performed via an S1 interface, not via a UE. The macro cell mayinclude the signal for avoiding interference on a component carrierbasis in the broadcast information and broadcast the broadcastinformation, so that a HeNB receives the broadcast information from themacro cell that is detected in the measurements of a surrounding radiowave environment to obtain the signal for avoiding interference on acomponent carrier basis. The method of obtaining the RACH configurationparameter from a macro cell by a HeNB, which has been disclosed in thefirst modification of the fifth embodiment, may be used as the methodfor this. A HeNB may perform measurements when the power of a HeNB isturned on, when it is initialized, or when it stops transmission.Alternatively, a HeNB may perform measurements in cycles or regularly.In the case of performing measurements in cycles or regularly, itsuffices that a HeNB avoids scheduling to a UE being served thereby toprevent self-interference.

As a result of avoiding interference on a component carrier basis asdescribed above, it is possible to reduce interference between a macrocell and a HeNB also in a case of a system that supports a largerfrequency bandwidth, such as LTE-A, whereby a high-speed andhigh-capacity communication can be provided.

The first embodiment to the sixth embodiment have disclosed the methodof notifying a HeNB of the HII by a macro cell as the method of reducinginterference between a macro cell and a HeNB. However, the macro celland HeNB can perform scheduling per cell, and accordingly at times, theinterference from a macro cell or the interference from a UE beingserved by the macro cell is desired to be avoided also in scheduling ofa HeNB.

In such a case, however, a problem that only a HeNB causes a reductionin communication rate or a reduction in communication capacity occurs ifthe macro cell merely instructs a HeNB to perform scheduling foravoiding interference.

In order to solve this problem, a HeNB notifies a macro cell of theinterference-related information that is the information related to theinterference to a physical resource such as the HII or OI, specifically,a signal for avoiding interference.

Normally, a macro cell (eNB) is less likely to be deployed in thecoverage of a HeNB. In many cases, a macro cell (eNB) is deployedoutside the coverage of a HeNB. That is, a HeNB is required to notify amacro cell (eNB) deployed outside the coverage of the own cell of thesignal for avoiding interference via a UE being served by the own cell.However, also in such a case, the appropriate use of the methodsdisclosed in the first embodiment to the sixth embodiment enables a HeNBto notify a macro cell of the signal for avoiding interference via a UE.

For example, in such a case, measurements of a macro cell cannot be usedas the method of limiting a macro cell to be notified of the HII by theHeNB. This is because in a case where a macro cell (eNB) is deployedoutside the coverage of a HeNB, the output power of the HeNB is normallysmaller than the output power of a macro cell, and thus the HeNB cannotbe detected at times even if the macro cell (eNB) measures a surroundingradio wave environment.

However, in order to solve this problem, the method of judging whetheror not a HeNB is deployed in the coverage of a macro cell, which hasbeen disclosed in the first embodiment, may be used as the method oflimiting a macro cell to be notified of the HII. As a result of themeasurements of cells nearby, the HeNB is allowed to judge a macro cell,in the coverage of which, the own cell is deployed.

Similarly to the HII notified HeNB list disclosed in the firstembodiment, the list of macro cells to be notified of the HII may beprovided such that a HeNB manages the macro cells to be notified of theHII using the list. It suffices that a HeNB judges a macro cell, in thecoverage of which, the own cell is deployed, and adds or deletes themacro cell to or from the HII notified macro cell list depending on theresults.

As to a UE, via which the HII is notified, it may be a UE being servedby a HeNB through application of, for example, the method disclosed inthe first embodiment. Alternatively, it may be a UE with the highestreceived power from a macro cell through application of the methoddisclosed in the first modification of the first embodiment. Not limitedto this, the methods disclosed in the first embodiment to the eighthmodification of the first embodiment are applicable.

Similarly, as a result of the appropriate use of the methods disclosedin the second embodiment to the sixth embodiment in combination, a HeNBcan notify a cell deployed outside the coverage of the own cell of theinterference-related information that is the information related to theinterference to a physical resource such as the HII or OI, specifically,a signal for avoiding interference via a UE being served by the owncell. This enables to solve a problem that only a HeNB causes areduction in communication rate and a reduction in communicationcapacity, leading to an increase of the communication capacity as asystem.

A HeNB can notify a cell deployed outside the coverage of the own cellof the interference-related information that is the information relatedto the interference to a physical resource such as the HIT or OI,specifically, a signal for avoiding interference via a UE being servedby the own cell, which also enables to notify a signal for avoidinginterference between macro cells and between HeNBs via a UE. As aresult, the interference or communication quality can be kept properlyalso in a situation in which a large number of macro cells or localnodes will be deployed in a complicated manner.

The methods disclosed in the present invention are applicable not onlyto HeNBs, but also to normal eNB (macro cell) and so-called local nodessuch as pico eNB (pico cell), node for hotzone cells, relay node, andremote radio head (RRH). For example, also in a case where a pico cellis deployed in the coverage of a macro cell, it is possible to performscheduling in which interference between the macro cell and the picocell is avoided by performing the methods disclosed in the presentinvention. Those local nodes correspond to small-scale base stationdevices.

Also in the case where various types of cells are deployed in a macrocell, the methods disclosed in the present invention are applicable. Forexample, as disclosed in the first embodiment, the measurement resultsof all of the detected cells may be reported without judging the type ofa cell that is detected by a macro cell. Not only HeNBs but also othertypes of cells are included, and thus a macro cell notifies those cellsof the HII. This enables to avoid interference with the other types ofcells. In addition, it is not required to receive the cell type inmeasurements, which simplifies the control of a UE and reduces powerconsumption. Further, the methods are applicable as the method ofavoiding interference between macro cells or between local nodes.

The use of the methods disclosed in the present invention enables toavoid interference as a system and prevent a reduction in communicationrate and interruption of communication. As a result, it is possible toavoid interference and keep the communication quality properly also in asituation in which an enormous number of macro cells or local nodes willbe deployed in a complicated manner.

While the LTE system (E-UTRAN) has been mainly described in the presentinvention, the present invention is applicable to the W-CDMA system(UTRAN, UMTS) and LTE-Advanced. Further, the present invention isapplicable to a communication system in which one or a plurality oftypes of nodes are used.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

DESCRIPTION OF REFERENCE SYMBOLS

-   -   1301 to 1313, 2201, 2207, 2213 UE, 1314 to 1321, 1324 to 1326,        2209 HeNB, 1322, 2204 macro cell (eNB), 1323 coverage of macro        cell 1322.

1. A mobile communication system comprising a mobile terminal, a basestation configured to perform radio communication with the mobileterminal, and a nearby base station other than the base station, whereinthe nearby base station notifies the base station of a parameter forperforming uplink transmission to the nearby base station by means of X2interface, the base station transmits the parameter for performinguplink transmission to the nearby base station to the mobile terminal,and the mobile terminal receives the parameter for performing uplinktransmission to the nearby base station transmitted from the basestation.
 2. The mobile communication system according to claim 1,wherein the parameter for performing uplink transmission to the nearbybase station includes a parameter relating to an initial transmissionpower of PRACH specific to a cell made up by the nearby base station. 3.The mobile communication system according to claim 2, wherein the mobileterminal determines the initial transmission power of PRACH using theparameter for performing uplink transmission to the nearby base station,and transmits the PRACH to the nearby base station.
 4. A mobile terminalused in a mobile communication system including the mobile terminal, abase station configured to perform radio communication with the mobileterminal, and a nearby base station other than the base station, whereinthe mobile terminal receives a parameter, of which the base station isnotified by the nearby base station by means of X2 interface, forperforming uplink transmission to the nearby base station.
 5. A basestation used in a mobile communication system including a mobileterminal, the base station configured to perform radio communicationwith the mobile terminal, and a nearby base station other than the basestation, wherein the base station is notified of a parameter forperforming uplink transmission to the nearby base station by the nearbybase station by means of X2 interface, and the base station transmitsthe parameter for performing uplink transmission to the nearby basestation to the mobile terminal.